Original subtitles

hi my name is mosh and i'm going to be

your instructor in this python course in

this course you're going to learn

everything you need to get started

programming in python python is one of

the most popular programming languages

and every day people use it to do cool

things like automation they use it in ai

as well as building applications and

websites like instagram and dropbox so

if you're looking for a job python is

for you in this course i'm going to

teach you everything you need to get

started with python we're going to talk

about all the core concepts in python

and then we're gonna build three python

projects together here's the first

project we're gonna build you're gonna

learn how to create this beautiful

website for an imaginary grocery store

here on the home page we can see all the

products in the shop and we also have an

admin area for managing the stock we're

going to build this using a popular

python framework called django now if

you have never built a website before

don't worry i will teach you everything

from scratch you're also going to learn

how to use python in machine learning or

artificial intelligence so you will

learn how to write a python program that

will predict the kind of music that

people like based on their profile just

like how youtube recommends videos based

on the videos you have watched before

i'll also teach you how to use python to

automate boring repetitive tasks that

waste your time you will write a python

program that will process thousands of

stretches in under a second i've

designed this python course for anyone

who wants to learn python if you're a

beginner don't worry i will hold your

hands through this entire course you're

not too old or too young and python is

super easy to learn you can write your

first python program in literally

seconds plus i'm going to give you

plenty of exercises to help you build

your confidence writing cool python

programs my name is mosh i'm a software

engineer with two decades of experience

and i've taught over 3 million people

how to code i'm super excited to be

teaching you python in this course so i

hope you stick around and learn this

beautiful and powerful programming

language

this tutorial i'm going to show you how

to download and install python on your

computer so the first thing i want you

to do is open up your browser and head

over to

python.org

on this page click on downloads here you

can see the latest version of python

currently at the time of recording this

video the latest version is python 3.7.2

chances are in the future when you're

watching this tutorial there is a newer

version of python available don't worry

all the materials you're going to learn

in this course will apply to the latest

version of python as well so let's go

ahead and download python 3.

all right now look at your downloads

folder here we should have python 3

installer simply double click that

if you're on windows you're going to see

this checkbox here

add python to path this is really

important make sure to tick this box

otherwise you're not going to be able to

follow this tutorial

if you're on a mac you're going to see

an installer like this with this setup

wizard we can install python 3 on our

computer so simply click continue and

again and again i agree with the license

agreement

and install it

this is going to take a few seconds so

i'm going to pause the recording

all right we have successfully installed

python3 on our computer let's close this

all right next we need to install a code

editor we use a code editor to write our

code just like how we use microsoft word

to write documents we use a code editor

to write code now there's so many code

editors out there the one that i'm going

to show you in this tutorial is pycharm

that is one of the most popular code

editors for writing python code you can

get it from jetbrains.com

pycharm

now more accurately pycharm is

considered an ide which is short for

integrated development environment and

that's basically a code editor on

steroids it has some additional features

that makes it really easy to rate code

so let's go ahead and download pycharm

now here on the download page you can

see two versions of pycharm one is the

professional edition which has

additional features and you'll have to

pay for them the other is the community

edition that is absolutely free and

that's what we're going to use in this

tutorial so go ahead and download this

as well

now once again look at your downloads

folder here you should have pycharm so

double click this

now if you're on windows you're going to

see an installation wizard simply click

next next next until you install pycharm

if you're on mac you need to drag and

drop this icon onto the applications

folder so drag and drop

all right now let's double click this to

run it

the first time you run pycharm you're

gonna get this warning because this is

an application that you download from

the internet so let's go ahead and open

it

next you're gonna see this dialog box

for importing some settings leave this

to do not import settings it doesn't

really matter

okay on this page select i've never used

pycharm you can see some keyword

shortcuts that might be useful in the

future just accept this and down the

bottom click the next button

and then next again

one more time and finally start using

pie chart

so here's the main page of pie chart

that you're going to see every time you

open it click on create new project

this is the location for our project

let's call this project hello

world

now before clicking create expand this

item here

make sure that base interpreter is set

to python 3.

python interpreter is basically a

program that knows how to execute python

code it will interpret or translate

python instructions into instructions

that a computer can understand now mac

computers by default come with an older

installation of python that is python 2.

it's considered legacy which means it's

no longer maintained or supported so

earlier we downloaded python3 make sure

that this is set to python3 if not from

this list select python 3.7

all right now let's go ahead and create

this project

now here right click on hello world

folder and go to new

python file

call this file app.pi

so by convention all python files should

have this pi extension

all right let's go ahead

now let's collapse this project panel by

clicking here and write our first python

program simply type print pr int all in

lowercase open and close parenthesis and

inside this parenthesis add quotations

you can either use single quotes or

double quotes

now in between the codes write your name

i am mash hamadani so let's write that

here

so this is your first python program

with this piece of code you can print

your name on the screen

now to run this go on the top

under the run menu click run also note

that there is a shortcut associated with

this command when i program i always use

shortcuts because that increases my

productivity so here on a mac computer

the shortcut is control option and r on

windows is different so let's go ahead

with that now it's asking where you want

to run this click on app

now down below

you should see this little terminal

window this is like a little window into

our program so here we can see the

results or output of our program in the

future as you learn more python you'll

be able to build applications that have

a graphical user interface or gui that

is a little bit complicated so for now

we're going to use this little terminal

window to see the results of our program

so as you can see my name is printed

here now as you write code this window

might get in the way so you can always

resize it or minimize it by clicking

this icon here

so this was our first python program now

if you didn't see the result i showed

you in this video use the comment box

below and tell me what error you

encountered i'll do my best to help you

move forward

in this python tutorial we're going to

take this program to the next level

we're going to make it more interesting

so i'm going to show you how to draw a

dog here

as part of this tutorial you will learn

how python code gets executed and you

will also learn about a few programming

terms

so press enter and on line two write

another print statement so print open

and close parenthesis add a quotation

now here we want to draw a dog so i

don't know that is the head of our dog

followed by four hyphens one two three

four so this is the body all right now

one more time

another print statement with quotations

now we need to draw the legs so add a

space

followed by four vertical bars so like

this

so here's a little imaginary dog now

let's run this program and see what we

get so in the top right corner you

should see this play button click that

there you go so we have our name and

right below that we have our imaginary

dog

now what you need to understand here is

that our python code gets executed line

by line from the top

so earlier i told you about python

interpreter that is the program that

knows how to translate or interpret our

python code into instructions that a

computer can understand so when we run

this program by clicking this icon here

python interpreter starts executing or

running our program line by line from

the top so first it executes line one

then moves on to line two and so on

so this is how python programs get

executed now let me show you something

cool let's add another print statement

with quotations now in between the

quotations add a star or an asterisk

like this now after the quotation and

before the parenthesis add a space once

again add an asterisk space

10.

what is going on here

well

anywhere we have quotations like here or

here we're defining a string a string is

a programming term which means a series

of characters so here we have a string

we also have a string on line three

as well as line two and line one

now here we are multiplying the string

by number 10. so this is the

multiplication operator just like the

multiplication operator we have in math

so with this piece of code we can draw

10 asterisks on the terminal let me show

you so let's run this program one more

time there you go

so we have 10 asterisks

now what we have here this piece of code

here

is called an expression an expression is

a piece of code that produces a value so

when py's interpreter tries to execute

line 4

first it will evaluate the code that we

put in between parentheses so it will

evaluate our expression our expression

will produce 10 asterisks and then those

asterisks will be printed on the

terminal

now as an exercise you can use this

print statement to draw another shape

you can draw a heart a ball whatever you

like i will see you in the next tutorial

one of the questions i get a lot on my

channel is how long does it take to

learn python and become job ready well

there is no single answer it really

depends on you and how much effort and

commitment you want to put into this but

i would say if you spend two hours every

day consistently

after about three months you should be

able to write basic python programs but

quite honestly that doesn't get you a

job

in order to get a job you need to

specialize in one area what do you want

to use python for do you want to use it

to build web applications or desktop

applications or do you want to use it in

machine learning and artificial

intelligence so whatever you want to do

you need to take additional courses for

example if you want to become a web

developer in addition to learning python

you should also learn about html css

some javascript and django which is a

popular python framework for building

web applications learning all these

things would take you another six months

so in total you need nine to 12 months

to become job ready at that point you

can get a junior developer job with a

salary of about 50 to 60 000 a year now

as you work more as you do more python

projects your resume starts to build and

you can ask for 100 000 a year or 120

000 a year depending on where you are

what company what geographical area it

really depends so there is no single

answer so are you excited to learn

python and get started on this career

path

if you are i would encourage you to make

a commitment and spend two hours every

day practicing python and use the

comment box below and let me know why

you're learning python what do you want

to do with it what's your dream job i

would love to hear your story

in this python tutorial you're going to

learn about variables which are one of

the most fundamental concepts in

programming they're not specific to

python they exist in pretty much every

programming language out there

we use variables to temporarily store

data in a computer's memory here's an

example let's type price equals 10.

when python interpreter executes this

code it will allocate some memory then

it will store the number 10 in that

memory and finally it will attach this

price label to that memory location

as a metaphor imagine we have a box in

that box we have number 10 and price is

the label that we put on the box

now we can use this label anywhere in

our program to access the value that we

have in that box this is a very

simplified explanation

so now let's print price on the terminal

print now this time we're not going to

add quotations because if we put

quotations here we will see the text

price on the terminal not the value of

the price variable so delete quotations

and type price

now let's run this program one more time

there you go so we see 10 on the

terminal

so this is how we define variables we

start with an identifier which is the

name of our variable then an equal sign

and finally a value now more accurately

when this number 10 is about to be

stored in the memory first it will get

converted to its binary representation

so this number 10 that we have is in the

decimal system which has all the digits

from 0 to 9. computers don't understand

all these digits they only understand

zeros and ones so when we store the

number 10 in the computer's memory first

it will get converted to its binary

representation which would be a bunch of

zeros and ones like zero zero one zero

zero one whatever i don't know then it

would get stored in the computer's

memory so let's take this program to the

next level

on the second line we can update the

value of this price variable so we can

reset it to a new value like 20. now

when we run our program we should see 20

because as i told you before python

interpreter executes our code line by

line from the top so first we set price

to 10 then we reset it to 20 and finally

we print it on the terminal let's run

the program

there you go so we see 20 here okay

now these numbers that we have here are

whole numbers without a decimal point in

programming we refer to these numbers as

integers so an integer is a number

without a decimal point

we can also use numbers with a decimal

point for example here on line 2 we can

define another variable called rating

and we set it to 4.9

now in programming refer to this kind of

number as a floating point number or

float for short so we have integers and

floats

we can also define a variable and set it

to a string for example

name equals mosh

we also have another kind of value which

is called boolean which can be true or

false they are like yes and no in

english here's an example i'm going to

define a variable is underline published

so we use an underscore to separate

multiple words in our variable's name

we set this to

true

or

false these are the boolean values

now note that python is a case sensitive

language which means it's sensitive to

lowercase and uppercase characters so

when defining variables we should always

use lowercase letters but here false and

true are special keywords in the

language so if we spell it with a

lowercase f python doesn't understand it

you can see we have a red underline here

which indicates an error so make sure to

spell this with a capital f or if you

want to set this to true make sure

t is capital

so in this program we are storing simple

values in our computer's memory simple

values can be numbers which can be

integers or floats or they can be

strings or booleans but in python we can

also store complex values like lists and

objects and that's what i'm going to

show you in the future

so before going any further i want you

to do a little exercise imagine we're

going to write a program for a hospital

so we're checking a patient named john

smith he's 20 years old and is a new

patient i want you to define three

variables here for his name his age and

another variable to tell if this is a

new or an existing patient so pause the

video and spend one minute on this

exercise when you're done come back

continue see my solution

all right so here we need three

variables the first one is the patient's

name

we said that to

john smith we can also call this full

name these are both valid names for our

variables

the second variable is for the age of

our patient so age is 20

and finally we need a variable to tell

if this is a new or an existing patient

that's where we can use a boolean value

so we define a variable is new and we

set it to true

so you have learned how to print

messages on the terminal window in this

tutorial i'm going to show you how to

receive input from the user so we're

going to write a small program that asks

the user's name and then it will print a

greeting message customized for that

user

so instead of prints we're going to use

input

now both this input and print are

functions that are built into python as

a metaphor think of the remote control

of your tv on this remote control we

have a bunch of buttons these are the

functions built into your tv you can

turn it on turn it off change the volume

and so on in python we also have a bunch

of functions for common tasks such as

printing messages receiving input and so

on so we're going to use the input

function

now whenever we have this parenthesis we

say we're calling or executing that

function it's like pressing a button on

a remote control so we're going to call

the input function

and in between parentheses we want to

add a string to print something on the

terminal

what is your name

with a question mark followed by a space

you will see why in a second

so this input function will print this

message on the terminal and then it will

wait for the user to enter a value

whatever the user enters this input

function will return so now we can get

that value and store it in the memory

using a variable so we get the result

and put it in a variable called name

okay

now on the second line we want to print

a message like hi john or hi mosh

whatever so print

quotations hi

with a space now after the quotation we

want to dynamically print

what we have in the name variable so we

add

a plus sign and then name

so here we have hi which is a string

we're concatenating or combining the

string with another string that is what

we have in the name variable

so here's another example of an

expression remember what is an

expression it's a piece of code that

produces a value so this expression

concatenates or combines two strings

let's run this program and see what

happens so run

okay here's the question what is your

name

mosh now note that earlier we added a

space after the question mark we did

this so

here in the terminal window the cursor

is separated from the question mark

otherwise it will be so close so let's

type whatever here press enter now we

get this message hi mosh

now here's a little exercise for you i

want you to extend this program and ask

two questions first ask the person's

name and then their favorite color and

then print a message like mosh likes

blue

so pause the video do this exercise and

then come back continue watching

all right so here's the first question

right after that we're going to call the

input function one more time this time

we're going to ask a different question

what is your favorite

color

now we get the new value and store it in

a variable called color or we could call

it favorite underline color either works

and finally we're going to change what

we pass to the print function

so first we print the name

then we concatenate this with a string

here we're going to type likes

we also put one space before and after

likes and once again we concatenate this

with the favorite color so

favorite color

now let's run this program

so what is your name

mosh enter favorite color blue enter

we get this message mosh likes blue

hey guys marsh here i just wanted to let

you know that you really don't have to

memorize anything in this course because

i put together a cheat sheet with

summary notes so you can quickly review

the materials in this course the link is

below this video

so i have done my best to create the

best possible python course on youtube

and i really appreciate it if you

support my hard work by liking this

video and sharing it with others so they

can learn as well and be sure to

subscribe to my channel for more

tutorials like this alright now let's

move on to the next tutorial

in this python tutorial we're going to

write a program that will ask the year

we were born in and then it will

calculate our age and print it on the

terminal so let's start with our input

function input

let's print birth year followed by a

colon and a space

now let's get the return value and store

it in a variable called birth underline

year

so as i told you before we use an

underscore to separate multiple words

next we need to calculate the age so we

define another variable called age

and here we do some basic math currently

we are in 2019. so let's write an

expression like this 2019 minus birth

year

now finally let's print

age on the terminal let's run our

program and see what happens so

my birth year is 1982.

enter oops we got an error what is going

on here

so whenever you say this red message

that means there is something wrong in

your program with the information here

we can find exactly where the error

occurred so

next to the file you can see the file

that generated this error in this case

that is

app.pi so currently our program has only

a single file but real complex programs

often have hundreds or even thousands of

files so in this file on line two this

is where we got this error and right

below that you can see

the piece of code that generated this

error so that is where we're calculating

the h and right below that you can see

the type of the error in this case we

have a type error and here's the message

unsupported operand types for

subtraction

and and

stir

so int is short for integer and that

represents a whole number

and stir is short for string so here

we're subtracting a string from an

integer and python doesn't know what to

do with it let me explain so i'm going

to close the terminal window

so after the first line is executed we

have this birth year variable set to a

string so whatever we type in the

terminal is always treated as a string

even if we type a number in other words

when we run this program this burst year

variable will be set

to a string

with four characters one nine eight two

this string is different from the actual

number 1982 one is an integer the other

is a string

right so

back to line two

where this error occurred

at runtime which means when we run our

program this expression on the right

side of the assignment operator is going

to look like this

2019

minus

string 1982.

python doesn't know how to interpret or

how to evaluate this expression

to fix this problem we need to convert

this 1982 into an integer and then we'll

be able to subtract it from 2019 and

that is very easy so far you have

learned about two built-in functions one

is print the other is input we have a

few more functions for converting values

into different types so we have int for

converting a string into an integer we

also have float for converting a string

into a float or a number with a decimal

point and we also have bool for

converting a string into a boolean value

so

to fix this problem

we need to go back on line two

and

pass this birth year variable to the int

function like this

int parenthesis like this

so we pass this string to the in

function int will convert it to an

integer and then

python interpreter will be able to

evaluate this expression now let's run

this program one more time

so birth here is 1982 enter so i am 37

years old

in python we have a useful function for

getting the type of variables for

example let's print the type of birth

year so right after line one let's print

now here we're going to call another

built-in function called type

and now let's pass

birth year

okay now similarly after line three

let's also print the type of h so print

type of age

okay let's run our program

so birth here one more time 1982

okay here's the result so the type of

burst year as you can see

is a class of stir or string

we'll look at classes in the future so

for now don't worry about them and also

below that you can see that the type of

the age variable is int or integer

so here's what you need to take away

whenever you use the input function you

always get a string so if you're

expecting a numerical value you should

always convert that string into either

an integer or a float

but here's a little exercise for you i

want you to write a program ask the user

their weight and then convert it to

kilograms and print it on the terminal

so pause the video do the exercise and

when you're ready come back continue

watching

all right so let's use our input

function

and ask for the weight

in pounds

here we get the weight

in lbs or pounds

now we need to convert this into

kilogram that is very easy so we define

another variable weight underline

kilogram or kg we set this to

weight underline lbs

times

0.45

and finally let's print weight

on the line kilogram let's run this

python program and see what happens

so my weight is 160.

all right once again we got an error

can't multiply sequence by non-end of

type float so as i told you before this

input function returns a string so we

cannot multiply a string by a float

python doesn't know what to do with it

so in this case we should convert this

number to an integer or a float and then

multiply it by 0.45

so let's call the int function

and pass weight underline lbs and run

our program one more time

160

okay so i am 72 kilograms

in this tutorial you're going to learn

more about python strings so i've

defined this course variable and set it

to python for beginners now earlier i

told you that you can use both single

and double quotes to define a string but

there are times that you have to use a

specific form otherwise you're going to

run into issues here's an example

imagine we want to change this string

into python's course for beginners so we

want to add an apostrophe like this

pythons

course

for beginners you can immediately see

this is going crazy

because our string starts here and then

terminates here all these characters

that we have after the second apostrophe

python interpreter doesn't know what

they are so to solve this problem we

need to use double quotes to define our

string so we can have a single quote in

the middle of the string so let's change

this to double quotes now you can see it

adds another double quote to close it we

have to manually remove this

and also one more time at the beginning

of the string

we need to add another double quote now

you can see the error is gone so if we

print

course

we see

python scores for beginners

beautiful now let's say we don't want

this apostrophe here so we have python

for beginners but we want to put

beginners in double quotes

once again if you add a double quote

here python interpreter gets confused

because it assumes the second double

code indicates the end of our string so

it doesn't know what these characters

are

so to solve this

we need to change our double quotes to

single quotes like this and then we can

add double quotes in the middle of the

string

now let's run this program

there you go so we get python for

beginners

so these are the cases for using single

or double quotes now in all the examples

i've shown you so far we only deal with

short strings but what if you want to

define a string that is multiple lines

for example what if you want to define a

string for the message that we send in

an email in that case we need to use

triple quotes so let me delete this

now we add three quotes so one two three

there you go

so we have three quotes to start our

string and three to terminate it again

these codes can be single or double

quotes okay

now with this we can define a string

that spans multiple lines for example we

can say hi john

here is our first email to you

thank you

the support team

like that

now

let's run this program and

here's the result so

we get this beautiful multi-line string

now let's change this back to something

simple

so we can look at other characteristics

of strings in python so i'm going to use

single quotes and set the course name to

python for beginners

here we can use square brackets to get a

character at a given index in this

string let me show you so to get the

first character we use square brackets

and type zero so the index of the first

character in this string is zero in

other words this is how

python strings are indexed zero one two

three 4 and so on so the index of the

first character is 0 the second

character is 1 and so on so let me

delete this and run this program

we get p

we can also use a negative index here

and this is one of the features that we

don't have in other programming

languages as far as i know so with the

negative index we can get the characters

starting from the end so if i pass

negative 1 here assuming that 0 is the

index of the first character negative

one is the index of the last character

so when we run this program we should

see s let's run it

there you go we get s if we pass

negative two this will return the second

character from the end let's run it one

more time

now we get r because that is the second

character from the end okay

so pay close attention to this square

bracket syntax because quite often it's

the topic for online python tests or

university exams so if you're preparing

for a python test make sure to watch

this tutorial one more time and

understand exactly how this square

bracket syntax works

you can also use a similar syntax to

extract a few characters instead of just

one character for example

if we type

0 colon 3 python interpreter will return

all the characters starting from this

index all the way to the second index

but it does not return the character at

this index in other words

back to these indexes

so we have 0 1 2 3 and so on

when we run this program python

interpreter will return the characters

starting from index 0

all the way to index 3 but excludes the

character and index 3. so when we run

this python program we're going to see

pipe let me show you so i'm going to

delete this line

run this program there you go we get

pipe

now here we also have default values for

the start and end index so if we don't

supply

the end index python will return all the

characters to the end of the string

let's take a look so run this program

there you go we get python for beginners

but if we change the start index to

1

this will exclude the first character so

when we run this program we see

y-t-h-o-n so p is removed okay

now similarly we have a default value

for the start index so if we don't

supply the starting index

but add an end index like 5 python

interpreter will assume 0 as the

starting index so let's run this program

there you go we get python

now what if we leave

both the start and end index well i told

you that in this case 0 will be assumed

as the start index and the length of the

string will be assumed as the end index

so with this syntax we can basically

copy or clone a string in other words if

i define

another variable here let's call it

another and set it to course square

brackets with just a colon now this

expression will return all the

characters in the course variable so

this second variable will be a copy of

our first variable let's take a look so

let's print another

and run our program there you go we get

python for beginners

so once again this square bracket syntax

is pretty important

if you're preparing for online python

tests or college exams make sure to

watch this tutorial again

now here's a little exercise for you i'm

going to delete all this code

define a variable called name and set it

to jennifer

now when we print

name

of

one

colon negative one what do you think

we're going to see on the terminal i

want you to use your knowledge to tell

what we're going to see on the terminal

without running this program so pause

the video think about it for a few

seconds and then come back continue

watching

so this expression will return the

characters starting from index 1 which

is the second character

all the way to the first character from

the end but excluding the character at

this index in this case the first

character from the end is r so r will be

excluded in other words we're gonna see

all the characters starting from e all

the way

to the second e

let's take a look so i'm gonna run this

program

there you go this is what we get and i

hope you guessed you're great

in this tutorial we're going to look at

formatted strings in python programming

language formatted strings are

particularly useful in situations where

you want to dynamically generate some

text with your variables let me show you

let's say we have two variables first

name and last name so first we set this

to john

and last we send this to smith now it's

better to call these variables first

name and last name because they're more

descriptive but here i'm using shorter

names because i want you to see the

entire code on the screen

so let's say with these two variables we

want to generate some text like this

john

in square brackets smith

is a coder let's say we want to print

this on a terminal how do we do this

well we define another variable like

message

now here we add the first name now we

need to concatenate this with a string

that contains a space and a square

bracket

next we need to add the last name

then we need to add a string that

contains the closing square bracket

followed by is a coder

okay so then

if we print message

and run this program

we see john smith is a coder right

now

while this approach perfectly works it's

not ideal because as our text gets more

complicated it becomes harder to

visualize the output

so someone else reading this code they

have to visualize all these string

concatenations in their head this is

where we use formatted strings they make

it easier for us to visualize the output

so

i'm going to define another variable

let's say msg short for message and set

this to a formatted string a formatted

string is one that is prefixed with an f

so f

quotes

now in between the quotes first we want

to add the value of the first name

variable so

we add curly braces and here we type

first

next we add a space we add our square

brackets in between the square brackets

we want to display the last name so once

again we add curly braces

and type last and finally here we type

is a coder so this is what we call a

formatted string

with these curly braces we're defining

placeholders or holes in our string and

when we run our program these holes will

be filled with the value of our

variables so here we have two

placeholders or two holes in our string

one is for the value of our first name

variable and the other is for the value

of the last name variable

now compare this format a string with

string concatenation with this formatted

string we can easily visualize what the

output looks like right now let's print

this on the terminal to make sure we get

the exact same output so let's print

message there you go so john smith is a

coder

so to define formatted strings prefix

your strings with an f and use curly

braces to dynamically insert values into

your strings

in this python tutorial i'm going to

show you some really cool things you can

do with python strings

so let's start by defining a variable

course

and we set that to python

for beginners

now to calculate the number of

characters in this string we can use a

built-in function called len so len

we give it this course variable and then

we can print the result let's run this

program

so as you can see we have 20 characters

in this string this is particularly

useful when we receive input from the

user for example you have noticed that

when you fill out a form online

each input field quit often has a limit

for example you might have 50 characters

for your name so using this len function

we can enforce a limit on the number of

characters in an input field if the user

types in more characters than we allow

them we can display an error okay

now

this len function

is another function built into python

it's a general purpose function so it's

not limited to counting the number of

characters in a string in the future

when we look at lists i'm going to show

you that we can use this function to

count the number of items in a list so

it's a general purpose function

now we also have functions specific to

strings for example we have functions

for converting all these characters to

uppercase or lowercase to access these

functions we use the dot operator let me

show you so

first we type course then dot

look these are all the functions that

are specific to strings

now in more accurate terms we refer to

these functions as methods this is a

term in object-oriented programming that

we'll look at in the future but for now

what i want you to take away is that

when a function belongs to something

else or is specific to some kind of

object we refer to that function as a

method for example here we have this

function

upper for converting the string into

upper case now more accurately because

this function is specific to strings we

refer to this as a method in contrast

len and print are general purpose

functions they don't belong to strings

or numbers or other kinds of objects

okay

so this is the difference between

functions and methods

now let's look at this upper method so

let's print the result

and run our program there you go we get

all these characters displayed in

uppercase now note that this method does

not change or modify our original string

in fact it creates a new string and

returns it so

if we print

our course variable right after we call

the upper method you can see that our

course variable still has its original

form so let's run this program one more

time there you go look this is our

original course variable it's not

modified

now similar to the upper method we have

another method for converting a string

into lowercase so let me show you print

course dot lower

now let's run the program

so on the second line you can see all

characters are in lower case

now there are times that you want to

find a character or a sequence of

character in a string in those

situations you can use the find method

so let me delete this reliance

we call course dot find

here we pass a character let's say p

and this will return the index of the

first occurrence of that character let

me show you so let's print the result

we get zero

because the index of the first capital p

in our string is zero

as another example if we pass a

lowercase o here

let's see what we get

we get four

because the index of this o here is 4.

now note that the find method is case

sensitive so it's sensitive to lowercase

and uppercase characters as an example

if we pass an uppercase o here and run

this program we get negative 1 because

we don't have an uppercase o anywhere in

the string

okay we can also pass a sequence of

characters for example we can pass

beginners

with a capital b

let's run this program

we get 11 because the word beginners

starts at index 11.

now we also have a method for replacing

a character or a sequence of characters

and that is called replace so let's

change find to replace let's say we want

to replace beginners with absolute

beginners so we add a comma to pass a

second value to this function or more

accurately this method we add a string

here i'm going to pass absolute

beginners

okay

now let's run this program

so we get python for absolute beginners

again this method like the find method

is case sensitive so if we pass

beginners all in lowercase this method

is not going to find this exact word in

our string so it's not going to replace

it with absolute beginners let's take a

look so i'm going to run the program one

more time look we still get python for

beginners we can also replace a single

character for example we can replace

capital p with

let's say capital j

now when we run this program we get

jython for beginners so these are the

find and replace method

and one last thing i want to show you in

this tutorial there are times that you

want to check the existence of a

character or a sequence of characters in

your string in those situations you use

the in operator so let's say we want to

know if this string contains the word

python we can write an expression like

this

string python

space

in space course so we're checking to see

if python is in the course variable now

this is an expression that produces a

boolean value like a true or false so we

refer to this expression as a boolean

expression

now if we print this on the terminal

we should get true and by the way let me

delete the second line we don't need it

anymore so run the program we get true

but if i change this capital p to a

lowercase p

and run the program we get false because

we don't have this exact sequence of

characters in our string now note that

the difference between the in operator

and define method is that our find

method returns the index of that

character or sequence of characters but

the in operator produces a boolean value

do we have this or not

so that's the difference now let's

quickly recap all the cool things you

learn to do with strings in this

tutorial

we can use the len function to count the

number of characters in a string this is

a general purpose function built into

python we also have specific functions

for strings which we referred to as

methods these include

upper for converting a string into

uppercase we also have lower

and title methods

you learn about the find method which

returns the index of a character or

sequence of characters we have the

replace method for replacing characters

and words in a string and finally you

learned about the in operator so

some characters in

a string

so you have learned that in python

programming language we have two types

of numbers integers which are whole

numbers like 10 they don't have a

decimal point and floating point numbers

or floats which are numbers with a

decimal point

now in this tutorial we're going to look

at the arithmetic operations supported

in python language these are the same

arithmetic operations that we have in

math we can add numbers multiply them

and so on so let's look at a few

examples we can print

10

plus 3.

so this is the addition operator we also

have subtraction we have multiplication

we have two kinds of division here's one

with a forward slash let's run this

program and see what we get

we get a floating point number but we

also have another division operator for

getting an integer so

if we add another slash here and run

this program

we get an integer

we have another operator called modulus

which is a percent sign and this returns

the remainder of the division so when we

run this program we should get 1.

there you go

and one last operator we have here is

exponent which is the power

so that is indicated with two asterisks

and this will return 10 to the power of

three so let's run this program we get a

thousand

so these are the arithmetic operators in

python programming language now for all

these operators that you learned we have

an augmented assignment operator that is

very useful let me show you so

let's say we have a variable called x we

set it to 10. now we want to increment

this by three we'll have to write code

like this x we set this to x plus three

so python interpreter will add 10 to

three the result is 13 and then it gets

stored into x again so when we print x

we should see

13. there you go

so this is how we can increment a number

right now augmented assignment operator

is a way to write the same code but in a

shorter form this is how it works

we type x

plus equals three what we have on line

three is exactly like what we have on

line two

so this is what we call the augmented

assignment operator we have augmented or

enhanced the assignment operator

now in this particular case we are

incrementing a number using the

augmented assignment operator but we can

also subtract or multiply a number by a

given value for example let's delete

what we have on line two

we can type

subtract equal three so here we are

subtracting three from x

when we run this program we should see

seven

there you go

now let me ask you a question

i'm going to clear all this code here

define x and set it to 10

plus 3 times 2. what do you think is the

result of this expression this is a very

basic math question that unfortunately a

lot of people fail to answer

the answer is 16. because in math we

have this concept called operator

precedence which means the order of

operations

so the multiplication operator has a

higher precedence so it's applied first

which means three by two is executed

first the result is six and then it's

added to 10. that is why x should be 16

after we run this code let's verify that

so print x run the program x is 16.

so this is what we call operator

precedence it's just a basic math

concept it's not about python

programming language so all the other

programming languages behave the same

way

so here's the order first we have the

exponentiation which is the power like 2

to the power of 3 then we have

multiplication

or

division

and finally we have addition or

subtraction

this is the order of operations let me

show you another example here i'm going

to add

the exponentiation operator so

2 to the power of 2. once again what do

you think is the result of this

expression pause the video and think

about it for a few seconds

the answer is 22

because the exponentiation operator

takes precedence so first 2 to the power

of 2 is executed the result is 4. then 4

is multiplied by 3

that is 12 and finally 12 is added to

10. so x should be 22.

so let's run this program and verify

this so i'm going to delete these lines

here

run the program there you go x is 22.

now let me bring back these rules here

we can also use parentheses to change

the order of operations so if we have

parenthesis

it always takes priority

in this case we can add parenthesis

around 10 plus 3 so this piece of code

will be executed first the result is 13

then the exponentiation operator will be

executed so 2 to the power of 2 is 4 and

finally 4 is multiplied by 13.

now here's a little exercise for you

i'm going to set x to parenthesis 2 plus

3 times 10 minus 3. what is the result

of this pause the video and think about

it for a few seconds

so you learn that parenthesis always

overwrites the order so this piece of

code is executed first the result is 5.

then between the multiplication and

subtraction you know that multiplication

takes precedence so next 5 will be

multiplied by 10 the result is 50 and

finally we have the subtraction so 50

minus 3 will be 47. let's verify this

print x

run the program there you go i hope you

guessed it right

so this is all about operator precedence

it's a very important topic and i see it

quite often in python tests so if you're

preparing for a python test make sure to

watch this tutorial one more time

in this tutorial we're going to look at

a few useful functions for working with

numbers let's start by defining a

variable like x and set it to

2.9 now to round this number we can use

the built-in round function so we call

the round function give it x and then

print the result let's run this program

so we get three we have another useful

built-in function called abs which is

short for absolute and this is the

absolute function that we have in math

we give it a value and it always returns

the positive representation of that

value even if that value is negative

here's an example let's call

the abs function and give it negative

2.9 when we run this program we're going

to see 2.9 on the terminal so let's go

ahead there you go so absolute always

returns a positive number now

technically in python we have a handful

of built-in functions for performing

mathematical operations if you want to

write a program that involves complex

mathematical calculations you need to

import the math module

a module in python is a separate file

with some reusable code we use these

modules to organize our code into

different files as a metaphor think of a

supermarket when you go to a supermarket

you see different sections for fruits

and vegetables cleaning products junk

food and so on each section in the

supermarket is like a module in python

so in python we have this math module

which contains a bunch of reusable

functions for performing mathematical

calculations so let me show you how to

use this module on the top

we type

import

math all in lowercase with this we can

import the math module now math is an

object like a string so we can access

its functions or more accurately its

methods using the dot operator so if you

type math dot look these are all the

mathematical functions available in this

module for example we can call the seal

method to get the ceiling of a number so

if we pass 2.9 here

and then print the result we should see

three let me delete all this other code

here all right let's run this program

there you go so we get three

another useful method is the floor

method so let's give that a try floor of

2.9 what do you think we're gonna get

we get two

now there's so many functions built in

this module and we don't really have

time to go through all of them but let

me show you how you can learn about them

on your own

open up your browser and search for

python3 math module make sure to add the

version python3 because the mass module

in python 2 is slightly different from

the math module in python 3.

so python 3 math module

now here you can see the documentation

for this module let's go

let's have a look if you scroll down you

can see the list of all the functions

and their explanation

so as an exercise i encourage you to

spend five minutes have a quick look at

this documentation see what functions

are there for you in case you need them

in this tutorial i'm going to talk to

you guys about if statements in python

if statements are extremely important in

programming and they allow us to build

programs that can make decisions based

on some conditions so if some condition

is true we're going to do certain things

otherwise we're going to do other things

here's an example

over here i've got this text file with a

bunch of rules for our program

if it's a hot day perhaps you want to

tell the user it's a hot day so make

sure to drink plenty of water

otherwise

if it's cold so here's another condition

if this condition is true we're going to

tell the user it's a cold day so wear

warm clothes

and otherwise if it's neither hot or

cold we want to tell the user it's a

lovely day

so let me show you how to write a

program that simulates these rules

so

back to our program here we start by

defining a boolean variable

is underline hot we set this to true

next we add an if statement so if

here we need to add a condition in this

case we're going to use our boolean

variable so is underline hot

now if this evaluates to true then we're

going to do certain things in this case

we want to tell the user hey it's a hot

day drink plenty of water

so back to our program

after our condition we add a colon

now note that when i press enter pycharm

automatically indents our cursor

now any code that we write here will be

executed if this condition is true

otherwise it will be ignored here's an

example

let's write a print statement

here i'm going to use double quotes

because i want to use an apostrophe in

our string so

it's a hot day

now let's press enter you can see the

cursor is still indented that means we

can write more code that will be

executed if this condition is true in

this case let's say we don't want to

write any extra code so to terminate

this block we need to press shift and

tab now the cursor is at the beginning

of the line so let's write a print

statement with a message like enjoy your

day

now when we run this program because

this condition is true we're going to

see this message followed by the second

message take a look so run

there you go it's a hot day enjoy your

day but if i go over here

and change this boolean value to false

and run the program again

our first message disappears and we only

see the second message enjoy your day so

this is how if statements work now back

here we can add another print statement

let's say

drink

plenty

of water now because this print

statement is also indented it will be

executed if this condition is true so

i'm going to revert is hot to true and

run the program one more time

there you go so it's a hot day drink

plenty of water and enjoy your day

all right now let's add a second rule

here if it's hot we're going to execute

these two lines otherwise if it's not

hot we want to print a different message

so here

we remove the indentation

and type else

colon

now when we press enter

once again our cursor is indented so the

code that we write here will be executed

if this condition is not true

so here we can print

it's a cold day

print

wear

warm clothes

now let's run our program one more time

so we get the messages about a hot day

followed by enjoy your day we don't see

any messages about a cold day now if we

go back here on the top

and

change this boolean value to false and

run our program

we see different set of messages it's a

cold day wear warm clothes and enjoy

your day

but there's a problem with our program

if it's not hot it doesn't necessarily

mean that it's cold maybe it's a lovely

day so the absence of heat doesn't mean

it's cold

back to our conditions

here on line four we have this rule that

says if it's a cold day then print these

messages otherwise if it's neither hot

or cold then say it's a lovely day so to

implement this rule we need to go back

to after pi

and define another variable so

let's say is underline called

we set this to

true

now here we need to add a second

condition so after

our first if statement we can use an

elif statement to define a second

condition here's how it works

so l if which is short for else if or

otherwise if now here we add another

condition so is called

so if it's cold you want to execute

these two lines

so let's cut these from here and move

them

under our second condition

and finally if none of these conditions

are true you want to print a different

message

it's a lovely day

so

right now

is hot is false is cold it's true so

when we run this program python

interpreter is going to execute the

first if statement in this case because

our condition is false these two lines

will be ignored then python interpreter

will look at line seven it will evaluate

this condition in this case is called is

true so we're going to see these two

messages on the terminal

now in this case because one of these

conditions was true this else statement

will be ignored so we are not going to

see this message and finally as before

we are always going to see this message

so let's run our program there you go

it's a cold day

wear warm clothes and enjoy your day

now

back to the top if we change is cold to

false

it's neither hot nor cold so it's going

to be a lovely day let's run the program

and

here you go it's a lovely day enjoy your

day

so this is the basic of using ip

statements as you can see they're very

useful in programming and with this we

can build all kinds of rules into our

programs

okay here's an exercise for you imagine

the price of a house is one million

dollars now if the buyer has good credit

they need to put down 10

of the price of this property otherwise

they need to put down 20

write your program with these rules and

display the down payment required for a

buyer with good credit you will see my

solution next

all right let's define a variable for

the price of this house so price we set

this to 1 million so one with six zeros

next we need a variable to tell if this

buyer has good credit

so has

good

credit and we set this to true

now we need an if statement so

if has

good credit is true

colon

here we need to calculate the down

payment so down underline payment

should be equal to 0.1 times the price

that is 10

of the price of this property

otherwise

colon

the down payment should be

0.2

times price

and finally we remove the indentation

and print

here we can use a formatted string

first we add a label

down payment colon and right after that

we add a placeholder or a hole for our

down payment variable so

curly braces

down payment

let's run this program

so down payment for a buyer with good

credit is 100 000

now let's improve this by adding a

dollar sign before this number so

back to our formatted string just before

the curly brace

i'm going to add a dollar sign let's run

this one more time that is better

in this tutorial i'm going to talk to

you guys about the logical operators in

python we use these operators in

situations where we have multiple

conditions here's an example

let's say we're building an application

for processing loans if an applicant has

high income

and good credit then they're eligible

for loan so in this example we have two

conditions one is having high income and

the other is having good credit so if

both these conditions are true then the

applicant is eligible for loan so this

is where we use the logical

and operator we use this operator to

combine two conditions and by the way

this is not specific to python

programming language pretty much any

programming language that supports if

statements also supports the logical

operators so back to our program let's

define two variables

has high income

we set this to true

and another one has

good

credit we also set this to true

now our if statement if

has high income is true

and

has

good credit is also true

then

we're going to print

eligible

for loan

so this is where we're using the and

operator

so if both these conditions are true

then this message will be printed if one

of them is false we're not going to see

this message let's try this out so i'm

going to run this program

so we see eligible for loan but if we

change

either of these conditions to false

and run the program again

look the message disappeared so this is

the logical and operator we also have

the logical or and we use that in

situations where we want to do certain

things if at least one of the conditions

is true for example let's change

the rule for this program such that

if the applicant has high income

or good credit then they're eligible for

loan

so if either or both these conditions

are true then the applicant is eligible

now

back to our program we can implement

this rule by using the logical or

operator so we simply replace

and with or

now when we run this program we're going

to see this message because at least one

of our conditions is true

let's take a look

so the applicant is eligible for loan

because they have good credit if we

change this to false

but set the other condition to true

and run the program we still see the

same result but if both these conditions

are false

then we're not going to see this message

anymore

so this is the difference between these

operators with the logical and operator

both conditions

should be true

with the logical or operator at least

one condition should be true

we also have another logical operator

called not and that basically inverses

any boolean value we give it if we give

it a true boolean value it converts it

to false for example let's make up a new

rule

if applicant

has good credit

and doesn't have

a criminal

record

then they're eligible for a loan let me

show you how to implement this so we go

back to our program

in this example we don't need the first

variable so let's delete that let's set

this variable to true

we also define another variable like has

criminal

record

and we set this to false

now we want to check to see if this

applicant has good credit and not a

criminal record this is where we use the

nut operator so

if they have good credit

and

not

criminal

record

so in this example

has criminal record is set to false when

we use the not operator this basically

gets changed to true so we'll have two

conditions that are true here's one and

here's another one so our applicant is

eligible for loan

and when we run this program we see

this familiar message

however

if an applicant has criminal record so

let's change this to true

now when we run this program we can see

our applicant is not eligible because

when we apply the not operator on this

variable

will get false so true changes to false

and will end up with two conditions one

is true and the other is false so the

result is false and that's why this

message is not printed

so this is all about the logical

operators in python

in this tutorial i'm going to talk to

you guys about the comparison operators

in python we use comparison operators in

situations where we want to compare a

variable with a value for example if

temperature is greater than 30 then we

want to print it's a hot day

otherwise if it's less than 10 it's a

cold day

otherwise it's neither hot nor cold and

by the way here i'm talking about

celsius not fahrenheit so to build these

rules into our program we need to use

comparison operators

back to app.pi

i'll define this temperature variable

let's write an if statement if

temperature

now we want to check to see if this is

greater than 30. so we use the greater

than operator if this is greater than 30

we want to print

it's a hot

day

otherwise

let's just print it's

not a hot day

now when we run this program we're going

to see the second message because 30 is

not greater than 30. so our first

condition

evaluates to false

let's verify that's a run

it's not a hot day okay

now if we change the temperature to 35

and run this again

we're going to see a different message

it's a hot day so this is where we use

comparison operators now what we have

here as you know is an expression

because it's a piece of code that

produces a value so more accurately this

is a boolean expression

so this is the greater than operator we

also have greater than or equal to

we have less than

less than or equal to

here's the equality operator so if the

temperature equals to 30 then we can say

it's a hot day note that this is

different from the assignment operator

that has only one equal sign you can see

if we use one equal sign here we

immediately get this red underline

because this is simply an assignment

statement we're changing the value of

the temperature we're setting the value

of the temperature variable to 30. we're

not comparing it with something else so

we don't have a boolean expression we're

not producing a boolean value okay so

our equality operator has two equal

signs and finally we have not equal

which is an exclamation followed by an

equal sign

now here's an exercise for you you've

probably seen that when you fill out a

form online sometimes the input fields

have validation messages for example

let's say we have an input field for the

user to enter their name now if the name

is less than three characters long we

want to display a validation error like

name must be at least 3 characters

otherwise if the name is more than 50

characters long then we want to display

a different validation error like name

can be a maximum of 50 characters

otherwise if the name is between 3 and

50 characters

then we just want to tell the user that

name looks good

so go ahead and write a program to

implement these rules

all right let's define a variable called

name and set it to let's say j so we're

assuming this is what the user types

into an input field

now we want to get the number of

characters in this string so we use the

len function right

lan of name

when we print this

we get one right you have seen this

before now here we want to use an if

statement so if len of name

is less than three

then

we want to print

name must be

at least

three characters

like here we need a second condition to

check the upper limit so l if

len of name

is greater than 50

then we want to print a different

message name

must be a maximum

of 50

characters

okay

and otherwise so else if none of these

conditions is true that means the name

looks good so print

name looks good let's run our program

so in this case we get this message

because our name is too short

if you go back here

and

type something really really long

and then run our program

we're going to see a different message

name must be a maximum of 50 characters

and finally

if we type a proper name here like john

smith

and run our program

we get name looks good

here's another good exercise that

combines many of the materials you have

learned so far so earlier you built a

program to convert someone's weight from

pounds to kilograms now we want to

extend this program and allow the user

to enter their weight in either

kilograms or pounds and then we'll

convert it to the other unit here's how

our program is going to work so i enter

my weight in pounds so 160.

now it's telling me is this in pounds or

kilograms so here i need to enter l for

pounds or k for kilograms and by the way

this program is not case sensitive so

whether i enter a capital l or a

lowercase l it takes it as pounds

now it tells me you are 72 kilos

let's run this program one more time

this time i'm going to enter my weight

in kilos so

72 is the weight

and the unit is kilograms okay

and it says you are 160 pounds so go

ahead and spend a few minutes on this

exercise you will see my solution next

all right first let's ask the user their

weight so we use the input function

weight colon

we get the return value and store it in

a variable called weight now the second

question

so one more time we use the input

function

l for pounds

lps or

k

for kilograms

so let's get that 2 and store it in a

variable called unit

now we need an if statement so if

unit

equals l

then we need to convert this weight into

kilograms however with this

implementation we are only allowing the

user to enter a capital l if they enter

a lowercase l this code is not going to

work

so this is where we use the upper method

of string objects so this unit is a

string because as i told you before the

input function always returns a string

so we can use the dot operator to access

all its methods or functions here we

call the upper method this will convert

whatever the user enters to uppercase

and then we'll compare it with a capital

l

now if this condition is true

then we need to get the weight and

multiply it by 0.45

however as you know this weight is a

string object and we cannot multiply a

string by a floating point number we

talked about this earlier in this course

so first we need to convert this weight

to a numerical value

so right here when we call the input

function we can get the return value and

pass it to the int function

so we call the in function

and

give it the return value of the input

function

now the in function will return an

integer so we can store it in this

weight variable

so here's the converted weight let's

store it in a variable called converted

then we print

here we can use a formatted string so

we prefix the string with f

u r

we add curly braces

to dynamically insert the value of

converted variable

and finally we add kilos

otherwise

if the unit is kilogram we need to

divide the weight by

0.45

so once again we type converted equals

to

weight divided by

0.45 and just to refresh our memory this

division operator returns a floating

point number but if we use double

slashes we'll get an integer

in this case i want to get a floating

point number

so

finally let's print

a formatted string

ur

curly braces

converted

pounds

okay

now let's run this program and see what

happens

weight is 160

in pounds

and that equals to 72 kilos perfect if

we run it one more time

and enter 72

kilos

we get 160 pounds

in this tutorial i'm going to show you

how to use while loops in python we use

while loops to execute a block of code

multiple times and they're often useful

in building interactive programs and

games in a future tutorial i'm going to

show you how to build a simple game

using a while loop

so let's get started with the basics

we write a wild statement and right

after that we type a condition followed

by a colon

as long as this condition is true the

code that we write in this block will be

repetitively executed here is an example

we can define a variable

like i as in short for index and set it

to 1.

now we set our condition to i less than

or equal to 5. so as long as i is less

than or equal to 5 we can print i

on the terminal and then we need to

increment i by one so we set i to i plus

one the reason we do this is that if we

don't do this i will be one forever so

we'll end up with an infinite loop

because this condition will always be

true 1 is always less than 5. so in

every iteration of this loop we

increment i by 1 so at some point i is

going to be 6 and then that is when this

condition will be false and then we'll

jump out of this loop okay

now to demonstrate how everything works

after this loop i'm going to add a print

statement

say done so note that these two lines

are indented so they are part of the

while block

okay now let's go ahead and run this

program to see what happens

so

take a look we get the numbers 1 to 5

followed by

done

so here's how this program gets executed

first we set i to one now python

interpreter executes line two this

condition is true because i is less than

five so

i is printed on the terminal and then

incremented by one

then the control moves back to the

beginning of the while loop so it

doesn't go to the next statement

so we come back here now we are in the

second iteration in the second iteration

i is 2 and because 2 is less than 5 our

condition is still true so i will be

printed on a terminal and once again it

will be incremented by 1. so at some

point i is going to be 6 and that's when

this condition will be false so our loop

will be terminated and then this dom

message will be printed on the terminal

so this is the basics of while loops now

let's make this program a little bit

more interesting

here we can write an expression like

this

we add a string

and in this string we add an asterisk

and then we multiply this string by i

so with this expression we can repeat a

string when we multiply a string by a

number that string will be repeated for

example if i is 2

this expression would produce

a string with two asterisks

okay now let's run the program and see

what we get so we get this little

triangle shape here because in the first

iteration i is one so

one times an asterisk produces one

asterisk

in the second iteration i is two so when

we multiply two by one asterisk we'll

get two asterisks

in this tutorial i'm going to show you

how to use a while loop to build a

guessing game like this

so we have this secret number which is

currently set to nine now the computer

is asking me to make a guess so let's

say one

it's not right because the secret number

is nine i can try again two

no it's not right let's try again so i

only have three chances to make a guess

if i can't guess the number the program

tells me that i failed let's run the

program one more time this time i'm

gonna guess the number so it's nine

there you go it says you win so let's go

ahead and build this program using a

while loop

all right let's start by defining a

variable to store our secret number so

we call that secret underline number and

set it to 9.

now we need a while loop to repeatedly

ask a user to make a guess

so while

condition cola

what is our condition here

well we want to give our user a maximum

of three guesses so similar to the last

tutorial we can define a variable like i

set it to zero and assume this

represents the number of guesses the

user has made

and then we can write our condition as i

less than

3.

note that here i'm not using less than

or equal to operator because with this

condition our loop will be executed four

times while i is 0 1 2 and 3.

so here we should use the less than

operator now if we give this code to

someone else it's not quite clear what

does i represent here it's only in r

head that i represents the number of

guesses the user has made so as a best

practice always use meaningful and

descriptive names for your variables so

it's better to rename this variable to

guess count let me show you how to

rename

so right click on i variable

and then go to refactor

and rename look at the shortcut on a mac

computer that's shift and f6

now in this dialog box we can easily

rename a variable and pycharm will

update all the references to that

variable so we don't have to manually

update each instance okay let's change

this to

yes underline count

enter there you go now that is better

also it's better to store three in a

separate variable to make our code more

readable because it's not quite clear

what does three represent here so

let's define a variable called guess

limit and set it to three

and then we can change three to guess

underline limit now our code is more

readable while guess count is less than

guess limit see it reads like a story

this is how you should write code

all right

so while this condition is true you want

to ask the user to make a guess so here

we use our input function

guess

now whatever the user enters comes out

as a string so we need to convert it to

an integer so right here we pass the

result to the end function

and then get it and store it in a

separate variable called guess

so at this point the user made a guess

now we need to increment guess count so

guess count

we set it to plus equal one okay now we

need to check to see if the user made

the right guess so here we need an if

statement

if

what the user guessed

equals

our secret number again see our code is

so readable it's like a story you can

read it like plain english

so if this condition is true you want to

tell the user they won so print

you one

now let's go ahead and run our program

up to this point so

okay it's asking me to make a guess i'm

gonna make the wrong guess of one it

asks me again beautiful two one more

time three

okay what is missing in this

implementation is the message that tells

me that i failed we're going to take

care of it momentarily but let's run the

program one more time and make the right

guess so nine

okay it says you won but it's still

asking me to make a guess because our

while loop is going to get executed

three times look one and two

so we need to change our program such

that if the user makes the right guess

we need to terminate our while loop we

need to jump out of it

how do we do that

so over here if the user makes the right

guess

after we print this message we can use

the break statement to terminate a loop

when python interpreter sees this it's

going to immediately terminate our loop

it's not going to evaluate this

condition again

now let's run our program and see what

happens

so

i'm going to guess the right number

you want and look we were not asked to

make two more guesses beautiful

now the last thing that we need to add

here is the message that tells the user

that they failed if they couldn't guess

the right number

how do we do that well in python our

while loops can optionally have an else

part similar to the if statements so

earlier you learned that our if

statements can optionally have an else

part

like here

so

if this condition is true do this

otherwise do something else right in

this case our if statement doesn't have

an else part

now

similar to the if statements our while

loops our while statements can also have

an else part

so

right at this level

we can add an else block so else colon

and the code that we write here will get

executed if this while loop completes

successfully without an immediate break

in other words if the user guesses the

right number we break this loop we jump

out of it so the code that we write in

the else block will not get executed but

if the user cannot guess this number

we're never going to break out of this

loop so this load will be executed to

completion until this condition becomes

false in that case the code that we

write in the else block will get

executed and this is the perfect

opportunity for us to tell the user hey

you made three guesses but none of them

were right so

print sorry

you failed

now let's test our program one more time

so guess one two three

sorry you failed let's run it one more

time this time i'm going to make a wrong

guess

and then the right guess

we won and our loop terminated

immediately

all right now it's time for you to

practice what you have learned so far so

once again we're going to build a game

this game is a simulation for a card

game now our game doesn't have a

graphical user interface or gui and it

doesn't really matter for now our focus

is entirely on building the engine for

this game

so let's see how this program works when

we run this we get this little symbol

here

and our program is waiting for us to

enter a command

if we type help either in lowercase or

uppercase it doesn't matter we get the

list of commands that our program or our

game currently supports so we can type

the start command to start our car we

can type the stop command to stop our

car and quit to terminate the game any

other commands that we type our program

is going to tell us hey i don't

understand that for example if i type

asd here

it says i don't understand that if we

type start

we get this message car started ready to

go if you type stop

it says car stopped and finally if we

type quit

our program terminates this is a

fantastic exercise for you to practice

what you have learned so pause the video

and spend five to ten minutes to build

this program

all right we're going to start with a

while loop

with a condition

what is our condition here

we want to run this loop until the user

types quit so we can define a variable

for storing the command that the user

enters and then we can run this loop as

long as the command does not equal to

quit

so right before the loop we define a

variable command and initially we set it

to an empty string an empty string is a

string that has no characters in it we

only have the quotes okay

so

then we type out our condition as

while command does not equal to

quit then

do something

now immediately we have a problem here

because we're assuming that the user

types the command in lower case so if

they type this in uppercase our program

is not going to behave properly so to

fix this problem we need to call the

lower method of the string object and

then compare the result

with this quit we could also call upper

and then type quit in uppercase it's a

matter of personal preference in this

demo i'm going to use lowercase

characters so okay

now in this loop we need to ask the user

to enter a command so once again we're

going to use our input function

we add a greater than symbol

followed by a space whatever the user

enters we get it and store it in our

command variable

now apart from the quit command there

are three other commands that we need to

support start stop and help so here we

need an if statement to compare what the

user enters with one of the supported

commands

so

if command

that lower

equals start

then you want to print a message like

the car started so print

car started

ready to go it doesn't matter

now the second condition what if it's

not start maybe it's stop so

alif command that lower

equals

stop there you go then we print a

different message car stopped

now look at our code we have repeated

this lower lower lower multiple times

this is bad in programming we have a

term called dry which is short for don't

repeat yourself

so whenever you have duplicating your

code that means you are doing something

wrong so how can we solve this problem

well instead of calling the lower method

in each condition we can call it right

here when we get the input from the user

so this input function as you know

returns a string we can immediately call

the lower method on that string and with

this our command will always be in lower

case so we don't need to

call this method in every condition

look

we remove the duplication and also our

conditions are shorter and easier to

read there's also one more place we need

to modify so it's right here

that is better

now the third command we need one more

alif

if the command equals help

then

we want to show the commands that we

support so here we're going to print a

multi-line string

so we use triple quotes

like this

and give the user a guideline like this

so start

to start the car

stop

to stop the car

and quit

to quit

now finally we need an else part so if

what the user enters is none of these

commands we're going to tell them hey we

don't understand this

so

else colon

print

sorry i don't understand that

and by the way

note that here because i'm using double

quotes i can easily use a single quote

as an apostrophe okay

so

let's run our program up to this point

and see what happens

all right let's type start car started

beautiful stop

car stopped

help

we get this guideline but there's so

much indentation before our commands

we'll fix that in a second and finally

let's test the quit command

oops our program didn't work properly

here's the reason with this if statement

we're comparing the command with start

stop and help anything else will end up

here so that's why our program says it

doesn't understand that

so that's why our program says it

doesn't understand that command however

after this else statement the control

will be moved to the beginning of the

loop at this point our command is quit

so our loop will complete and the

program terminates in other words when

we run this program

and type quit

our program actually quits but we still

see this message which shouldn't appear

here how can we solve this problem well

we can come back here

and just before the else block add

another alif

something like this alif command

equals

quit

then we can immediately break

this will solve our problem but note

that we have kind of repeated this

expression in two places

the reality is we don't really need this

condition on the top because with this

if statements well more accurately with

this alif we can jump out of this loop

and terminate our program so we can

simplify our condition

to something like this true

so while true means this block of code

is going to get executed repeatedly

until we explicitly break out of it okay

now let's test our program one more time

so

quit

now our program terminates and we don't

see that message beautiful

so let's fix the last problem you saw

that when we typed help

these guidelines appeared with so much

indentation and here's the reason look

right here in our code they're already

indented so when we use triple quotes

what we type here will be printed

exactly as is

so because we have indentation here this

indentation will also be printed on the

terminal so let's delete

these

okay run the program one more time

type help

the annotation is gone beautiful now

here's a challenge for you i want you to

take this program to the next level so

right now if we type start we get this

message car started and if we type start

again

we get the same message it would be

better if we got a message like car is

already started so it doesn't make sense

to store the car twice similarly

if we type stop

it says car stopped if we type it again

we get the exact same message it doesn't

make sense to stop a car twice so here's

what i need you to do if the car is

stopped and the user tries to stop it

again the program should say hey the car

is already stopped what are you doing

and similarly if the car is already

started and the user tries to start it

again the program should yell at the

user so go ahead and make the necessary

changes to implement this scenario

all right to add this to our program we

need to know if the car is started or

not so there is one more piece of

information that we need to store in the

memory what is the kind of data we need

to store here a boolean is the car

started or not it's a matter of yes or

no true or false so on the top

here we can define another variable like

started and initially we set it to false

so the car is not started right

now

when the user types the start command

here we need to check to see if the car

is already started if not we'll start it

otherwise we'll yell at the user so in

this block we write another if statement

if it's already started

then we print

car is already started

otherwise so we add an else statement

here

and at this point we set started to true

so we start the car and print this

message okay

now we need to make a similar change

for the stop command so if the car is

already stopped

we need to print a different message

if

not started so here we're using the not

operator to see if the car is stopped

so if it's not started that means it's

stopped okay

so if it stopped your print

car is already stopped

with double p's

otherwise so else

we need to stop the car how do we do

that we set started to false and then

we'll print this message

as easy as that let's go ahead and run

our program

so

initially our car is stopped so i'm

going to type stop

it says the car is already stopped so

let's start it

okay now our car is started let's start

it one more time

the program is yelling at us so we

cannot start a car twice beautiful now

let's stop it

it says the car is stopped let's stop it

one more time we get this message again

in this tutorial i'm going to talk to

you guys about for loops in python in

the last tutorial you learned about

while loops you'll learn that we use

while loops to execute a block of code

multiple times in python we have another

kind of loop that is a for loop and we

use that to iterate over items of a

collection such as a string because a

string is a sequence of characters so it

looks like a collection so we can use a

for loop to iterate over each character

in a string and then do something with

it here's an example we type out four

then we define a variable this is what

we call a loop variable in each

iteration this variable will hold one

item

so let's call it item

in here we type out a string like python

and then colon

so with this for loop we can iterate

over this string and in each iteration

this item variable will hold one

character at a time in the first

iteration it will be set to p then in

the second iteration it will be set to y

in the third iteration it will be set to

t and so on okay

so here we are inside our four block

because of the indentation here so

whatever we type here will be executed

in each iteration for now we can simply

print this item

now let's run this program and see what

happens

so you can see each character in our

string is printed on a new line

let's look at another example

in python we can define lists using

square brackets so let me remove this

string from here

and define a list using square brackets

a list is simply a list of items like a

list of numbers a list of customers a

list of emails products blog posts

whatever so here we can define a list of

names like mosh

john

sarah

and then go ahead run our program so you

can see in each iteration we get one

name

and print it on a new line

we can also loop over a list of numbers

for example

[Music]

one two three four let's run it

again we see each number on a new line

but what if we want to iterate over a

large list of numbers we don't want to

explicitly type out a list with let's

say a hundred or a thousand numbers but

i want to type 567 all the way to 100

that is when we use the range function

so let me delete this

in python we have a built-in function

called range for creating a range of

numbers so

we give it a number let's say 10. let's

run this program

now we can see here on the terminal we

have numbers 0

all the way

to 9. so 10 is not included so basically

when we call the range function this

range function creates an object it's

not a list it's a special kind of object

that we can iterate over in each

iteration this object will spit out a

new number we can also work with a range

of numbers here let's say we want to

start from 5

and go all the way to 10.

so

let's run our program

now we have the numbers 5 6 7 and 9.

also this range function can optionally

take a step so we can pass

to

as the step to this function

and when we run our program

you can see that our first number is

five now we go two steps forward to get

seven once again we go two steps forward

we get nine and that is the end of our

range so this is the basics of using for

loops in python

now here's an exercise for you i want

you to write a program to calculate the

total cost of all the items in a

shopping cart so let's say we have a

list of prices

like 10

20 and 30.

i wanted to use a for loop to calculate

the total cost of all the items in our

imaginary shopping cart so calculate

that and then print it on a terminal

that's pretty easy and you should do it

in a couple of minutes

so as you learned we use for loops to

iterate over all the items in a

collection a collection can be a string

it can be a list it can be a range

object that is returned from the range

function anything any kind of object

that has multiple items

so in this example we're going to use a

for loop to iterate over the list of

prices so for item in

prices colon and by the way this loop

variable we don't have to call this item

we can call it anything for example in

this case we can rename it to price so

for price

in prices

now in each iteration this price will

hold one value in the first iteration

it's going to hold 10 then it's going to

be 20 and then it's going to be 30.

so we need to define another variable to

calculate the total

so

we define that outside of a for loop

let's call it total and initially we set

it to zero

now in each iteration we get the current

price and add it to the total so

rate total equals total plus price or as

you learned earlier we can use the

augmented assignment operator to

simplify this code

so

after our for loop this total variable

has the total of all the prices we can

simply print it here

or we can use a formatted string so

a string prefix with f

we add a label like total curly braces

to dynamically include some value in our

string in this case our total

variable

so let's go ahead and run this program

there you go so the total cost of all

the items in our imaginary shopping cart

is 60.

in this tutorial i'm going to talk to

you guys about nested loops in python

using a nested loop basically means

adding one loop inside of another loop

and with this technique we can do some

amazing things for example we can easily

generate a list of coordinates so a

coordinate as you know is a combination

of an x and y value let's say 0 and 0.

now let's say we want to generate a list

of coordinates like this so we have 0

and 0 then we'll have 0 and 1 then 0 and

2

next

we're going to change x so we're going

to use 1 for the x and once again we're

going to use these three values for the

y coordinates so 1 and 0 then

1 and 1 and 1 and 2.

you got the point we can easily generate

these coordinates using nested loops let

me show you so we'll start with one loop

let's say for x in range four

with this loop we can generate values

for the x coordinate let's print this on

the terminal

okay

so we get the values 0 to 3.

now for each x like 0 we should generate

a few y values

so that is where we use a nested loop so

inside of this loop we're going to add

another loop so instead of just printing

x first we want to add

another loop

for y in range let's say 3

now we can print x and y together

so print here we use a formatted string

to display coordinates like this so we

add parenthesis

inside of this parenthesis first we need

to add x so curly braces x

then a comma

followed by

another set of curly braces and

y

let's run this program and see what we

get

there you go so we have these

coordinates 0 and 0 0 and 1 0 and 2.

then we have 1 and 0 1 and 1 1 and 2 and

so on so let me explain exactly how this

program gets executed

so in the first iteration of our outer

loop x is zero right

now we are on line two here we have a

new loop which we call an inner loop in

this inner loop in the first iteration y

is going to be zero

so we print 0 and 0 on the terminal now

the control goes back to line 2 or our

inner loop in this second iteration y

will be set to 1 but we're still in the

first iteration

of our outer loop so x is still 0 but

now y is incremented to one

so that is why we see zero and one on

the terminal once again the control goes

back to line two we are in the third

iteration of our inner loop so this will

continue until this inner loop completes

that is when y reaches two because this

range function generates number zero to

three but not including three so we'll

have zero one and two

after this inner loop completes then the

control goes back to line one at this

point we're going to be in the second

iteration of our outer loop so x will be

one then the control will be moved to

line two or our inner loop at this point

this range function is going to generate

the numbers 0 to 3 one more time so this

inner loop will be executed three times

and then we'll go back

to our outer loop so this is how nested

loops get executed

okay here's an exercise for you but this

one is a little bit more challenging

than the exercises you have done so far

so i really don't expect you to do it

but if you do it wow i will be so proud

of you

so see what i have done here

using nested loops i've written some

code to draw this f shape can you see

that

so let me give you a hint

first of all

we have this list

called numbers

in this list we have these values 5 2

five two two

these values determine the number of x's

we have on each line so for example the

first item in this list this tells us

that we should have five x's on the

first line there you go so one two three

four five

on the second line we're gonna have two

excess

on the third line we're gonna have five

excess like this

so i've written code to convert

a simple list of numbers into a shape

like this

now here's a tip for you

using a for loop you need to iterate

over this list in each iteration you get

one number this determines the number of

excess to be displayed on that

particular line so if you want to cheat

you can get this number and multiply it

by a string that contains x so if you

multiply x by five you'll get five x's

that's not what i want you to do i want

you to use an inner loop here to

generate a string that contains five x's

so imagine in python we cannot multiply

a string by a number so to solve this

problem we need a nested loop

so go ahead and spend five minutes on

this exercise and by the way do your

best to solve this it is a little bit

challenging but it's not extremely

difficult it just requires a little bit

of focus you'll see my solution next

all right so first we need to iterate

over all the items in this list

so for item in numbers

or we could rename this variable to

x underline count that is the number of

x's on each line okay

now i told you that if you want to cheat

you can write code like this print x

times x underline count if we run this

program

we get the same output

so this is the beauty of python with

python we can write expressions like

this we can multiply a string by a

number to repeat it a lot of other

programming languages don't support this

feature but for this exercise i wanted

you to imagine that we don't have this

feature in python so you would have to

use an inner loop to solve this problem

here's how it works

in the first iteration xcount is going

to be 5. so we need to generate five x's

how can we do that well let's say we

define a variable called output and

initially we set it to an empty string

now we need to add five x's to the

string so we can use another loop for

count

in range

of x underline count so we're using the

range function to generate a sequence of

numbers from 0

up to x count

so in our first iteration x count is

going to be five so range of five would

generate the numbers zero one two three

four so this inner loop will be executed

five times that is exactly what xcount

represents

so now

in each iteration we simply need to

append an x to our output variable so we

said output

plus equals x

and then

after this inner loop we simply print

the output

with this we'll print five excess on the

first row then we go to the second

iteration of our outer loop at this

point xcount is going to be 2.

now

on line 3 we're going to reset our

output variable to an empty string so we

start over

then we go to our inner loop this loop

will be executed two times so we'll

append two access to the output variable

and then print it

as simple as that so see it wasn't

really that difficult but it was

slightly more difficult than the

previous exercises

so let's run this program there you go

now if you're adventurous i want you to

modify the values that we have

in our

numbers list

to print an l here

now in this tutorial we're going to take

a closer look at lists

so i'm going to define a list of names

let's send them to john

bob

marsh

sarah and mary

so if we print

this list here

what we see on the terminal looks

exactly like how we define our list so

we have square brackets and in between

these square brackets we have our items

so we have five strings in this list

now we can also access an individual

element using an index just like how we

can access an individual character in a

string using an index

so here we type out square brackets and

specify an index the index of the first

item in this list is zero

so let's run this program there you go

we get john now if you want to print out

the third element in this list its index

is two

so

names of two

returns mosh

now we can also pass a negative index

here so negative one refers to the last

item in this list that is mary let's run

the program

there you go we see mary if you pass

negative 2 this returns the second item

from the end of the list

so let's run the program there you go we

get 0. so this is exactly like accessing

individual characters in a string we can

also

use a colon to select a range of items

for example if we pass

to colon this will get all the items

starting from the index of two that is

mosh here all the way to the end of the

string so let's run this program

there you go

we get this list with three items mosh

sarah and mary

we can also specify an end index let's

say 4 so this will return all the items

up to this index but it doesn't include

the item at this index so when we run

this program we only see mosh and sarah

the item at index four which is the

fifth element or the fifth item in this

list is not returned so mary is not

returned okay and also here we have

default values so if we leave out the

end index this expression is going to

return all the items starting from the

index of two to the end of the list or

if we leave out the start index this

expression assumes zero as the default

index so it will return all the items

from the beginning to the end of the

list okay and by the way just like

strings these square brackets here don't

modify our original list they simply

return a new list for example if we pass

two here

you can see this returns a new list with

three items so if we go back here and

print our original list of names right

after

you can see it's not affected so

whenever we use square brackets with a

colon to select a range of items we get

a new list and by the way we can also

modify any of the elements in this list

for example let's say we made a mistake

and the first item shouldn't be spelled

john with an h so we want to remove the

h that is very easy so we access it

using an index that is names of zero and

we set it to a new value

like this

now let's print our list

so you can see

the first item in this list is now

updated so this is the basics of lists

and here's an exercise for you i want

you to write a program to find the

largest number in the list this is a

fantastic exercise for beginners so go

ahead and spend a few minutes on this

and then come back continue watching

all right let's define a list of numbers

numbers

with a bunch of random numbers 3 6 2 8 4

and 10.

now to find the largest number in this

list we need to define another variable

let's call it max this variable will

hold the largest number now initially we

want to assume that the first item in

this list

is the largest number so we set max to

numbers

of zero we're only assuming that the

first item is the largest number chances

are our assumption is wrong so we need

to iterate over this list we need to

loop through it

get each item and compare it with max

if it's greater than max then we need to

reset max to that number so in the first

iteration we get 3 and max is also 3.

is 3 greater than 3 no so we move on we

get the second number is 6 greater than

3 it is so we need to reset max to 6.

once again we continue we get 2 is 2

greater than 6 no it's not so we move on

then we get 8 is 8 greater than six it

is so we should reset max to eight that

is pretty easy

so here we need a for loop for number

in numbers colon

now we need to check to see if this

number is greater than max

so

if number

is greater than max colon

then we need to reset max so we set max

to this new number

that's all we had to do so let's print

max

and run our program

we can say the largest number in this

list is 10. it doesn't matter whether

this number is at the end of the list or

at the beginning so if i move 10

and put it right at the beginning

we should still see the same result

let's run our program we still see 10 if

i put this somewhere in the middle

our program should still work let's put

it right after

two

run the program we still get 10.

in this tutorial i'm going to talk to

you guys about two-dimensional lists in

python two-dimensional lists are

extremely powerful and they have a lot

of applications in data science and

machine learning here's an example in

math we have a concept called matrix

which is like a rectangular array of

numbers let me show you so yeah one two

three four five six seven eight nine so

we have a rectangular array of numbers

we have rows

and columns so this is a three by three

matrix in math now we can model this in

python using a two-dimensional list a

two-dimensional list is a list where

each item in that list is another list

so

you want to define a matrix we set it to

a list

each item in this list is going to be

another list and that list represents

the items in each row

so the first item in our list is going

to be another list and in this list

we're going to have the values 1 2 and

3.

now the second item in our matrix list

once again we have a list this list

represents the items in the second row

so

4 5 and 6 and finally

7 8 9.

so as you can see we have a

two-dimensional list each item

in our outer list is another list

okay so this is how we can implement a

matrix in python now to access an

individual item in our matrix once again

we use square brackets let me delete

this stuff

all right

so how do we access one here well

we start with our list

then we add square brackets first we

need to go and get the first item in

this list right so we pass zero now this

expression returns another list that is

the inner list

in this list let's say we want to access

the second item

so

once again we add square brackets and we

pass one that is the index

of two in this list right

so if we print this on the terminal

we get two okay so using two square

brackets we can access individual items

in our matrix and also we can modify

these values using this syntax so

before printing this let's change it to

20. so matrix of 0 and 1 let's change it

to 20

and then print it there you go it's

modified

now here we can also use nested loops to

iterate over all the items in this

matrix let me show you so

we start with the rows for row

in matrix

so with this loop we are iterating over

our matrix list in each iteration row

will contain one list one item okay

now

here we need to use an inner loop

so we need to loop over this row which

is a list of items

we can type out four

item in row colon

and print item

okay

so let's run this program

there you go we get all the items

in our list

hey i just wanted to make a quick

announcement in case you haven't seen my

website yet head over to

codewithmosh.com this is my coding

school where you can find plenty of

courses on web and mobile application

development in fact recently i published

a comprehensive python course that goes

way beyond this beginner's course on

youtube and if you're serious about

learning python and getting a job i

highly encourage you to enroll in this

course just like this tutorial you can

watch it anytime anywhere as many times

as you want and you will also receive a

certificate of completion that you can

add to your resume and the course comes

with a 30-day money-back guarantee so if

you're not happy we give all your money

back no questions asked the price for

this course is 149

but the first 200 students can get it

for only 15 dollars so if you're

interested the link is below this video

click the link and get started

in this tutorial i'm going to talk to

you guys about the list methods or list

functions these are the operations that

we can perform on a list so let's define

a list of numbers

here we pass a bunch of random numbers

like 5

2

1 7 and 4.

now there are a number of things we can

do with this list we can add new items

to it we can remove existing items we

can check for the existence of an item

these are the operations that we can

perform on a list so when we type

numbers

dot we can see all these functions or

more accurately the methods that are

available in our list objects

so we can call the append method to add

a new item to this list let's say

13 actually no it's not a good number

i'm joking i'm not superstitious so

let's add 20.

it doesn't really matter and then print

our list

when we run the program you can see

20 is added at the end of this list but

what if you want to add a number

somewhere in the middle or at the

beginning of our list for that we use a

different method that is called insert

so

insert now this method takes two values

let me show you so when we open

parenthesis

look at this little tooltip above the

insert method

you see the first value that we need to

pass here is an index so this is the

index at which we want to insert this

new item let's say we want to add an

item at the beginning of our list so we

pass the index position of zero

and then the second value is the actual

object we want to add to this list let's

say we want to add the number 10.

now when we print this list you can see

that the number 10

is placed at the beginning of the list

and all the other items are pushed to

the right

we can also remove an item so we call

remove and pass the item that we want to

remove let's say we want to remove five

now we print our list so you can see

five is gone and we have two one seven

four if you wanna remove all the items

in the list you can call the clear

method so

clear

this method doesn't take any values so

we simply call it and it empties our

list

all the items are removed

we also have another useful method

called pop

and with this we can remove the last

item in a list let me show you so run

our program you can see the number four

is removed from the end of our list

now if you want to check for the

existence of an item in a list you can

call the index method so

we call index

and pass the value here like five and

this returns the index of the first

occurrence of this item so let's print

this on the terminal

we don't need this line anymore

so the index of five is zero what if we

pass a number that doesn't exist in this

list let's say 50.

run the program

we get an error we got a value error 50

is not in the list

there is also another way to check for

the existence of an item we can use the

in operator so

let me show you we type out 15 in

numbers

earlier we used the in operator with a

string we could check for the existence

of a character or a sequence of

characters in a string

now here we're checking for the

existence of 50 in the list of numbers

so let's print this

we get a boolean value false so unlike

the index method this expression doesn't

generate an error so it's safer to use

this we also have another method for

counting the occurrences of an item

let's say we have another five

over

here now we can call

numbers that count and pass five and

this should return two because we have

two fives in this list take a look there

you go

that is pretty useful now if you want to

sort your lists you can call the sort

method so

we call the sort method here this method

doesn't take any values so

look at the return value that is none

none is an object in python that

represents the absence of a value

so this sort method doesn't really

return any values it simply sorts this

list in place so instead of printing the

return value of this method

we simply call it to sort our list and

then print our list

take a look

now all the items are sorted in

ascending order we can also sort the

items in descending order so after we

sort the list we can call

the reverse method and this simply

reverses our list

now let's go ahead and run our program

take a look

our numbers are sorted in descending

order

and one last method i want to show you

here that is pretty useful is the copy

method so copy

with this method we can get a copy of

our list so let's define another

variable called numbers2

now numbers2 is a copy of our original

list so if you make any changes to our

original list if you add new items to it

if you remove existing items these

operations are not going to impact our

second list let me show you so after we

take a copy of our numbers list

let's add a new item to this list some

numbers that append 10.

so the first list is updated so now we

have a new item in our first list

then let's print the second list

take a look we don't have the number 10

here because these are two independent

lists

so these are all the operations that we

can perform on lists we can add new

items to a list we can remove existing

items we can check for the existence of

an item we can sort our lists and copy

them

now here is the exercise for this

tutorial i want you to write a program

to remove the duplicates in a list again

this is a fantastic exercise so spend a

few minutes on this and then come back

continue watching

all right let's say we have a list of

numbers with a bunch of duplicates so 2

2

4 6 3 4

6 1.

we want to remove the duplicates

so we need to define another list let's

call that unix

initially we set it to an empty list

then we need to iterate over

our first list get each item and if we

don't have that number in this unix list

then we'll add it to the second list as

simple as that so

for number in numbers

now we need to check to see if we have

this number

in the second list

so we use the in operator

if

number

not in unix

so note that here we are using the not

operator so if we don't have this number

in this unix list

then we'll need to add it so

unix dot append

number

that's all we have to do

so let's go ahead and print the unix

list

there you go so we have two four six

three and 1. the duplicates are removed

in this tutorial i'm going to talk to

you guys about another important

structure in python called topo tuples

are similar to lists so we can use them

to store a list of items but unlike

lists we cannot modify them we cannot

add new items we cannot remove existing

items we say tuples are immutable we

cannot mutate or change them let me show

you so i'm going to start by defining a

list of numbers one two three

so we use square brackets to define

lists and parentheses to define tuples

so if we change this to

parenthesis one two three now we have a

tuple so if we type numbers dot look

here we don't have the append or insert

methods so we cannot add new items to

this tuple we also don't have remove

clear and pop we cannot remove any of

these items here

we only have two methods count and index

we use count to count the number of

occurrences of an item and index to find

the index of the first occurrence of an

item so we can only get information

about a tuple we cannot change it and by

the way these other methods that you see

here they start with two underscores we

refer to this as magic methods they're

more of an advanced topic so they go

beyond the scope of this tutorial if

you're interested to learn about them

you can get my python course i've

covered them in detail

so similar to lists we can access

individual items using square brackets

so we can get the first item like this

and then print it on the terminal

there you go the first item is one

but if you try to change the first item

we'll get an error so numbers of zero we

set it to 10

and run our program there you go we get

this type error because the tuple object

does not support item assignment

so we cannot mutate or change tuples

they are immutable

now practically speaking most of the

time you will be using lists but tuples

are also useful if you want to create a

list of items and you want to make sure

that nowhere in your program you

accidentally modify that list then it's

better to use a tuple

in this tutorial i'm going to show you a

powerful feature we have in python

called unpacking so let's define a tuple

called coordinates

and here we pass three values one two

three so imagine these are the

coordinates for x y and z

now let's say we want to get these

values and use them in a few expressions

in a few complex expressions in our

program maybe we want to include them as

part of a large complex formula so

together we'll have to write code like

this coordinates of zero then let's say

we want to multiply this by coordinates

of one and then multiply it by

coordinates of two

our code is getting a little bit too

long this is just a very simple example

but let's say we want to use these

values in quite a few places in our

program so a better approach is to get

these values and store them in separate

variables like

we can get coordinates of 0 and store it

in x

then we get coordinates

a 1

and store it in y

and similarly we get coordinates of 2

and then store it in z

now instead of repeating coordinates of

2 or coordinates of 0 multiple times we

can simply work with these variables x

times y times z

that is better right

so nothing new so far but in python we

have a powerful feature called unpacking

and with that we can achieve the same

result with far less code so we can

define our variables x y

and z

and set them to our tuple

what we have on line six is exactly

identical to what we have on lines two

to four

so this is a shorthand to achieve the

same result

so let me delete this and explain how

this code works when python interpreter

sees this statement it will get the

first item in this tuple and assign it

to this variable then it will get the

second item in this tuple and assign it

to the second variable and similarly it

will get the third item in this top hole

and assign it to the third variable we

have here

so we are unpacking this tuple into

three variables

now if we print

x you can see

x is one similarly y

is two there you go

so this is unpacking and by the way this

is not limited to tuples we can use this

feature with lists as well so if i

change parenthesis

to square brackets

now coordinates is a list so we can

unpack this list into three variables

now

run our program you can see y is two

in this tutorial i'm going to talk to

you guys about dictionaries in python we

use dictionaries in situations where we

want to store information that come as

key value pairs here's an example think

of a customer a customer has a bunch of

attributes like name

email

phone number address and so on but each

of these attributes has a value for

example the name can be john smith the

email can be john gmail.com

the phone can be whatever so what we

have here is a bunch of key value pairs

so in this example our keys are name

email and phone and each key is

associated with a value so this is where

we use a dictionary with a dictionary we

can store a bunch of key value pairs

so let me show you how to define a

dictionary in python back to our program

i'm going to define a variable customer

and here we set it to curly braces with

these curly braces we can define a

dictionary in this example we have an

empty dictionary that doesn't have any

key value pairs now we can add one or

more key value pairs in between the

braces so let's add a key value pair

here

i'm going to set the key to name

and the value to john smith

then we add a comma to add another key

value pair so let's set

age to 30.

let's add another key value pair is

underline verified

and we set this to a boolean

now what matters here is that these keys

should be unique so if i add another key

value pair here

let's set age

to

40.

now look pycharm has highlighted the h

key because we have duplicated that and

that's not allowed so each key should be

unique in a dictionary just like the

dictionaries we have in the real world

in a real dictionary we have a bunch of

words and their definition each word is

listed only once in a dictionary we

don't have the word book twice

so let's delete this second duplicate

key value pair

so the keys should be unique and in this

example i'm using strings but they can

also be numbers we're going to look at

that later

but the value can be anything it can be

a string a number a boolean a list

literally anything

now we can access each item in this

dictionary using square brackets so

we type customer

square bracket and then specify a key

like name

and this will return the value

associated with the name key let's print

it on the terminal have a look

there you go so

the name is john smith now what if we

pass a key that doesn't exist

let's say

birth date

run the program we get a key error

because we don't have a key called birth

date also

if we spell name

with let's say a capital n we get the

same error because we don't have a key

with the exact

same sequence of characters in this

dictionary

now to get around this we can use the

get method let me show you

so instead of using the square brackets

we call the get method and specify

our key

now if we use a key that doesn't exist

here it doesn't yell at us for example

if you pass birth date

it simply returns the non-value earlier

i told you that none is an object that

represents the absence of a value

so instead of getting a key error we get

none now we can also optionally supply a

default value for example if this

dictionary doesn't have this key we can

supply a default value let's say

january 1st 1980.

let's run the program

now instead of getting none we get this

default value

so this is how we can access the value

associated with the key in a dictionary

we can also update these values for

example before our print statement we

can write code like this customer

of name

let's update the name to

jack smith

now this little warning here is telling

us that we could simply put jack smith

here instead of defining it once and

then update it don't worry about that it

doesn't really matter now with this line

if we print the name of this customer we

should see jack smith let me show you so

i'm going to use the square bracket

notation again let's print the name of

the customer you can see

that is updated here we can also add a

new key here

let's set the birth date

to some value like

january 1st 1980

and then we can print it here

so as you see we can easily add new key

value pairs to a dictionary

so this is the basics of using

dictionaries in python they're extremely

important and they have a lot of

applications in the real world

okay here's an exercise for you so here

we have this program that asks our phone

number let's type one two three four we

type it in digits and then this will

translate it to words take a look enter

it prints one two three four that's a

pretty cool program so go ahead and

spend a few minutes on this exercise

it's pretty easy i'll see you next

all right so first we need to get the

user's phone number we call the input

function

with the label phone we get the result

and store it

in this variable

now let's say the user enters one two

three four so we need to loop through

this string get each character and

translate it to a word

so what we need to implement this

scenario is a dictionary because a

dictionary is a structure that allows us

to map a key to a value so we can have a

dictionary with keys like one two three

four and we map each of these keys

to a word so we can map the digit one to

the word

one we can map two

to two you got the point so let's define

a dictionary we can call it digits

underline mapping

now this dictionary i'm gonna add a few

key value pairs

one we map it to one

two

to two

three to three and finally

four to four now technically we should

add all the digits from zero to nine but

i don't wanna waste your time typing

repetitive things here you got the point

so let's move on now we need to loop

through the phone string so

for

character

in phone

we get each character and then use it to

access a key value pair in our

dictionary so

digits underline mapping

we can use square brackets or call the

get method i would prefer to use the get

method so in case the user enters some

character that is not part of our

dictionary our program is not going to

yell at them

so

we call the get method

and pass this character as the key

and if we don't have this key we can

supply

a default value like an exclamation mark

so with this we'll get a word now we

need to add this word to an output

string so we can define an output string

initially we set it to an empty string

in each iteration we get this and add it

to our output string so we type output

plus equals

this

and we should also add a space at the

end

so the words are not close to each other

okay

that's all we have to do

now finally let's print this output

run our program so i'm going to type one

three four

five let's see what we get we get one

three four with an exclamation mark

in this tutorial i'm going to show you

something really cool that you can do

with dictionaries so here we have this

program we can type a message like good

morning

followed by a smiley face when we press

enter we get this beautiful smiley face

or

we can type

i am sad with the sad smiley face and it

gets translated to this beautiful emoji

so this is another application of using

dictionaries we have a dictionary that

maps these characters into smiley faces

so let's go ahead and build this program

together

we start by calling the input function

here we pass a greater than symbol as an

indicator for the user to type a message

we get that message store it here

as you know that is a string now we need

to split the string by a space

so if the user types good morning with a

smiley face we want to break this down

into three words good

morning

and smiley face

to do that we can call the split method

so

we call message dot split

and pass

a string with one space as the separator

what this method does is basically it

goes through the string and anywhere it

finds this character in this case a

space it uses that as a boundary to

separate this string into multiple words

and then it will return a list let me

show you so let's store that here words

and then print it

on the terminal

let's go ahead and run our program so if

we type good morning sunshine enter we

get a list with three items each item is

a string okay

now

back to our program we need to define a

dictionary for mapping special

characters like these two into a smiley

face

so

we can call that emojis

set it to curly braces here we add a key

value pair

a smiley face and we map that to

a string in the string we want to add an

emoji

if you're on a mac keyboard you can

press ctrl

command and space and this should bring

up this emoji box if you're on windows

honestly i really don't know how you can

do this but there must be applications

that do this for you so let's go ahead

and pick this

happy smiley face good now let's add

another key value pair for a sad face

we map this to

this

face here

good

so we have a list of words now we need

to loop through this list get each word

and potentially map it to an emoji so we

can write a for loop for word in words

now we want to go to our dictionary and

see if you have an item with this word

as the key

if you have an item with that key then

we'll get its value otherwise we want to

use the same word so if the user types

good morning we don't want to translate

those words we just want to return those

so that is the case where we use the get

method to supply a default value so we

want to get an item with the key

word and if we don't have an item with

that key we simply use that word as the

default value now similar to the

exercise that we did in the last

tutorial we need an output variable so

let's define that here output set it to

an empty string

now back to line 9

we get the return value of the get

method and add it to our output variable

so output

plus equals whatever we get from the get

method and finally we need to append a

space at the end

that's it we're done so let's print the

output

and run our program

i'm gonna type good morning sunshine

with a smiley face

we get that beautiful let's try a sad

face as well i am sad

too bad

beautiful so as you can see dictionaries

have a lot of use cases in real

applications

here's the solution from the last

tutorial where we created an emoji

converter now so far we've been writing

all our code right here in app.pi but as

our programs grow we need a better way

to organize our code we need to break up

our code into smaller more manageable

and more maintainable chunks which we

call functions

so a function is a container for a few

lines of code that perform a specific

task for example you have learned about

if you have the built-in functions in

python like print and

input each of these functions have a

purpose they know how to perform a

specific task

so when building large complex programs

we should break up our code into smaller

reusable chunks which we call functions

to better organize our code and that's

what i'm going to show you in this

tutorial so let's write a simple program

for printing a greeting message so we're

going to do a print

hi there

and let's add another message welcome

aboard

so here we have a simple program with

only two lines of code now let's say

these two lines potentially we're going

to need them in other programs so we can

put them in a function that we can reuse

let me show you how to do that so

we start

typing out def that is a reserved

keyword in python and it's short for

define when python interpreter sees this

it knows that we're defining a function

next we need to give our function a name

let's say greet

underline

user so all the best practices you learn

about naming your variables also apply

here which means you should name your

functions with lowercase characters if

there are multiple words you need to

separate them using an underscore and

you should always always always always

use meaningful and descriptive names for

your functions

so here we're defining a function called

createuser after that we need to add

parentheses followed by a colon now you

know that whenever we add a colon at the

end of a line we're telling python that

we're defining a block of code so when

we press enter the next line is indented

now any code that'd be right here will

belong to this function

so

i'm going to move these two lines these

two print statements inside of our

function we can simply press tab to

indent them beautiful also let's remove

this extra line break that is better so

these two lines

now are part of our greet user function

so whenever we call this function these

two lines will be executed okay now

let's remove indentation so here we are

outside of our function

let's do a print statement

and print start

after that let's call our function so

greet user

and finally let's do another print

statement

and print finish

now we have this little warning here

this underline

if you hover your mouse over this line

this tooltip is telling you that we

should add two blank lines after

function definition this is coming from

pep8 which is a document that defines

the best practices for formatting our

code we'll look at that in the future so

for now to make pycharm happy let's add

an extra line break after this function

so whenever we define a function we need

to add two line breaks after okay

so

now let's run our program and see what

happens all right so we get four

messages on the terminal first we get

the start message then we get the

messages coming from our create function

so hi there and welcome aboard and

finally we see the finished message

so let me explain the flow of our

program when python runs this code it

doesn't actually print these two

messages on the terminal because these

lines of code are inside of this

function so they will only get executed

if we call this function if we don't

call this function these lines will not

get executed okay

so the execution of our program actually

starts here the first message that we

see on the terminal is the start message

after that python sees that we're

calling the greet function so it will

jump over here and then execute these

two lines

then it will jump outside of this

function and continue the normal

execution of our program so it will

print the finished message on the

terminal

so this is how functions work

also note that the order of this code

matters so here we're calling the grid

function after we have defined it if you

try to call it before you define it you

will see an error for example

if we call

greet user function right here see we

immediately get this red underline which

says unresolved reference greet user

which basically means python doesn't

know what is this great user it's not

defined anywhere

so we always define our functions first

and then call that

here's the function we created in the

last tutorial now i got a question for

you what is the difference between

calling this function

and the print function of python

the difference is that the print

function takes some information in this

case the message that we want to print

but our grid function doesn't take any

information wouldn't that be nicer if

you could pass the name of the user here

and then instead of saying hi there we

could print the name of the user so in

this tutorial i'm going to show you how

to pass information to your functions

and that is pretty easy

so

back to the definition of our great user

function

inside of this parenthesis we can add

parameters these parameters are

placeholders for receiving information

for example we can add a name parameter

and with this we can pass the name of

the user when calling this function so

let's pass john here

now when we call this function and pass

this value this name parameter will be

set to john

so it will act like a local variable

that we define inside of this function

just imagine we didn't have this

parameter and instead we had a variable

like name that was set to john now here

we could simply print the name of this

user so we could use a formatted string

and print the value of the name variable

right now we don't really have this

local variable defined in this function

we have a parameter

it's exactly the same thing so with

these parameters we can receive

information in our functions now let's

go ahead and run this program

so take a look we get hi john welcome

aboard we can take this to the next

level now we can call this function one

more time

so greet user and this time supply a

different name let's say mary

so we are reusing our grid function and

passing it a different value

imagine if we didn't have this function

we would have to repeat this line twice

once for high john and another time for

hi mary so this is the benefit of

defining functions we can take a few

lines of code that have a specific

purpose and put them inside of a

function

so now let's run our program one more

time

there you go so we get hi john welcome

board then we get high mary welcome

aboard

now note that when a function has a

parameter we are obligated to pass a

value for that parameter so if we remove

john

from here

and run our program we get this type

error grid user missing one required

positional argument

argument in programming is the value

that we supply to a function so

back to this example

mary in this case is an argument that we

pass to the name parameter a lot of

programmers don't know the difference

between parameters and arguments and

think they are the same but they are not

parameters or the holes or placeholders

that we define in our function for

receiving information

arguments are the actual pieces of

information that we supply to these

functions okay

so let's bring back

this john string okay now we can also

define multiple parameters for example

let's rename this parameter to first

name as i told you before you can right

click here go to refactor and then

rename or preferably you can use a

shortcut so the shortcut for this on mac

is shift and f6

and this brings up the rename dialog box

here we can change this to first

underline name

now we can add a second parameter so

comma

followed by last underline name

so back to our formatted string let's

also print the last name beautiful so

here when calling this function then we

can supply

another argument

so john smith and let's delete

this line we don't really need it

anymore run our program take a look hi

john smith

so in the last tutorial you'll learn

that whenever we define parameters for

our functions we should always supply

values otherwise we'll get an error

let's look at that there one more time

so i'm going to delete the second

argument and only pass john

run our program

we get this message

greet user missing one required

positional argument

so these are arguments that we have here

like john and smith we refer to these as

positional arguments which means their

position or order matters in other words

the first argument we add here is the

value for the first parameter and the

second argument is the value for the

second parameter so if we change their

position or order we'll get different

result let's take a look let's pass

smith first and then

john okay

delete that's good let's go with this

so instead of getting high john smith we

get high smith john

so that is the reason we refer to these

arguments as positional arguments their

position or order matters but in python

we also have keyword arguments and with

those the position doesn't matter let me

show you how they work so let's say here

we want to pass john as the value for

the first name parameter we can simply

specify that here so first name equals

john

now what we have here is a keyword

argument

so this combination of having the

parameter name followed by its value is

what we call a keyword argument and with

these keyword arguments the position

doesn't really matter

so here we're supplying john as an

argument for the first parameter

now similarly we can use a keyword

argument for smith let me show you so

last name equals smith's

so now we have two keyword arguments so

with these keyword arguments we don't

have to worry about the order of the

parameters that doesn't mean we should

always use keyword arguments not really

most of the time we use positional

arguments but in certain situations

these keyword arguments help us improve

the readability of our code

so on line 7 it's quite clear that we're

supplying smith as the last name and

john as the first name

now in this particular example even if

we didn't have the keyword arguments

just passing two positional arguments

like john and smith would be sufficient

because it's easy to guess what is the

purpose of this argument but sometimes

you're dealing with functions and you're

passing numerical values to them in

those situations it may not be quite

clear what these values represent let me

show you an example let's say we have a

function for calculating the total cost

of an order so we can call that

calculate underlink cost

so when calling this function we need to

supply three pieces of information

one is the total cost of all the order

items let's say fifty dollars

the other is the shipping cost let's say

five dollars and the last piece is a

discount let's say 0.1

someone reading this code may not be

sure what these three values represent

in this case we can improve the

readability of this code by using

keyword arguments so we can prefix each

value with the name of the parameter

they target for example we can set total

to 50 and then shipping to 5 and

discount to 0.1

now if we give this code to someone else

they can immediately tell what these

values represent so that is the power of

keyword arguments so here's what i want

you to take away for the most part use

positional arguments but if you're

dealing with functions that take

numerical values see if you can improve

the readability of your code by using

keyword arguments you simply prefix the

arguments that you pass with the name of

their parameters and this will increase

the readability of your code now there

is one more thing you need to know about

keyword arguments these keyword

arguments should always come after

positional arguments let me show you

what i mean so

back to our simple create user function

let's use a keyword argument for the

first name

so

let's set first name to john and see

what happens look we immediately get

this error take a look positional

argument after keyword argument so when

calling this function we're supplying

one keyword argument and one positional

argument and python doesn't like this

so if you're mixing positional and

keyword arguments you should always use

the positional arguments first and then

the keyboard arguments

in other words let's remove this keyword

argument here

so john is now a positional argument is

targeting the first parameter right now

after this position argument we can

supply any number of keyword arguments

so if we set last name to smith look

python doesn't have any problem with

this because we're adding a keyword

argument after a positional argument so

let's quickly recap for the most part

use positional arguments if you're

dealing with functions that take

multiple numerical values and it's not

quite clear what those values represent

use keyword arguments to improve the

readability of your code and finally if

you're passing both positional and

keyboard arguments use the keyword

arguments after the positional arguments

so far you have learned how to create

functions and send them information

using their parameters

in this tutorial i'm going to show you

how to create functions that return

values this is particularly useful if

you're doing some kind of calculation

your function and you want to return the

result to whoever is using your function

let me show you so

let's start by defining a function

called square this function simply

calculates the square of a number

so we need to add one parameter here

that is our number

now here we want to calculate number

times number that is the square of a

number

now to return this number outside of

this function we simply use the return

statement so return

now our square function is very simple

it only has one line of code but in a

real program you might have a function

that has 10 lines of code to calculate

something so

this return statement is very valuable

with that we can return values to the

colors of our function

so with this when we call

the square function let's say we give it

3

now this function returns a value just

like the input function of python this

input function waits for the user to

type something and press enter and then

it will return the user's input as a

string so we can get it and store it

in a variable like this right we have

the same story with our square function

so our square function returns a value

we can simply get it and store it in a

variable let's call that result

now we can print

result on the terminal

there you go so result is nine we could

also

pass this function call directly inside

of the print function without defining a

separate variable sometimes this is

useful for writing shorter code so in

this case we don't really need this

result variable we simply want to print

the square of three

so we could simply pass this function

call

right here as an argument for the print

function

so let's delete this variable now our

code is shorter so with this we're

calling the square function this returns

a value and we'll pass that value as an

argument to the print function

okay

when we run this program we get the

exact same result there you go

now what happens if we don't use a

return statement in our function so in

the last example we simply used a print

statement let's temporarily

remove this return statement and

print the result on the terminal like

this

so let's run our program one more time

and see what we get we get two things on

a terminal the number nine and none what

is happening here

well when python interpreter executes

this code first it will call the square

function

so the control moves to the square

function here we calculate the square of

this given number and then print it on

the terminal that is the reason we see 9

right here

now by default all functions return the

value none

so if we don't have a return statement

here

by default python returns

none none is an object that represents

the absence of a value it's like nothing

or null in c c plus plus java and

javascript

so

in this example we didn't have a return

statement and by default python returned

none from this function

so after the square function is executed

the value none is returned and passed as

an argument to the print function that

is the reason we see

none on the second line

so here are the two things you need to

take away from this tutorial by default

all functions in python return none you

can change that so if you have a

function that calculates something you

can return the result using the return

statement

here's the code for our emoji converter

program that we wrote earlier if you

missed that tutorial make sure to go

back and watch it as i told you before

there is a table of content right below

this video in the description so you can

simply click on the emoji converter

tutorial to watch it

now your exercise is to reorganize this

code using a function so i want you to

extract a function in this code because

this algorithm for converting these

smiley faces into emojis is something

that we probably want to use in a lot of

different applications you can use it in

a chat application in an email

application and so on we don't want to

write all this code every time we want

to convert these characters into smiley

faces

so out of all these lines of code that

we have from line 1 to line 10 the lines

2 to 9 belong to our algorithm

all these lines together implement this

feature

so you should put these lines in a

separate function

now why don't we have the input in that

function because the input can come in

different forms currently we're using

the input function to receive the input

from the terminal but in other

applications we might receive the input

from a graphical user interface so the

input can come in different forms we

don't want to put that in our function

because this line will not be reusable

we want to give our function

the actual message as a string we don't

care how we got that message in one

program we might get it from the

terminal in another program we may get

it from a graphical user interface

so that is the reason this line of code

should not be in that function by the

same token

you shouldn't include the last line in

that function because what we do with

the output is different from one program

to another in this program we're

printing the output in another program

we might send that output as an email or

as a response in a chat application so

as a general rule of thumb your

functions should not worry about

receiving input and printing it these

lines of code should not belong to your

functions so go ahead and reorganize

this code by extracting a function

all right on the top first we need to

define our function so we type def

give our function a name like emoji

underline converter so the name of this

function clearly tells me what it does

each function should be responsible for

one and only one task and that task

should be clearly explained in the name

of the function okay

so our emoji converter function should

take a parameter we call that message

that is a string right

colon

now we need to move the lines five

all the way

to the end of our four block

into that function so

let's select all these lines

we can cut them from here by pressing

command and x on mac or control and x on

windows

then we paste them here

as you can see these lines are

automatically indented so they are part

of the emoji converter function if this

didn't happen on your computer make sure

to select these lines and use the tab to

indent them

all right so here's our emoji converter

function beautiful

now

after that

in the main flow of our program first we

get the input from the user

we store it in this variable message

and then

we call

emoji converter and pass this message

this function should return a value that

is what we calculate

at the end of this function so right

after this 4 block we need to add a

return statement return output

now that our function returns a value

we can get it and store it in a separate

variable let's call that result and then

we can simply print that here

or we can make this code shorter we

don't really need this variable here so

we can simply

call the emoji converter

and print the result

like this now here we have another line

because

as i told you before we need two blank

lines after our function definitions so

currently we have only one black line we

need to add

another black line

let's go ahead and run this program to

make sure everything works as before

so i'm going to type a message like good

morning with a smiley face

good let's run it one more time

i'm sad too bad okay beautiful

so here's the final

result we defined this function called

emoji converter this function takes a

parameter called message

and finally returns the output

in this tutorial i'm going to teach you

guys how to handle errors in your python

programs so let's start by writing a

small program to get the user's age from

the terminal so we call the input

function

input

add a label here

like age

this returns a string so we need to pass

it to the end function

and then store the result

in a variable called h

now let's print h to make sure we have

implemented everything properly

run our program

we type 20

20 is printed here beautiful now look at

the exit code of this program exit code

0 means our program terminated

successfully there were no errors but

what if we run this program

one more time and instead of entering a

numerical value we enter something like

asd

we get a value error

with this message invalid literal for

end with base 10. basically what this

message is telling us is that this

string asd does not contain a valid

whole number that can be converted to an

integer now look at the exit code of

this program exit code one means our

program crashed so zero always means

success and anything but zero means

crash

now as a good python programmer you

should anticipate these situations you

don't want to let your entire program

crash just because the user entered an

invalid value

so instead of letting the program crash

you should handle this situation and

print a proper error message and that's

what i'm going to show you in this

tutorial

now if we're going any further

look at the type of the error we get

here value error so remember this we're

going to get back to this shortly

now how can we handle these errors

in python we have a construct called try

accept

we use that to handle errors let me show

you how it works so

on the top we type try colon

now as you know we're defining a code

block so i'm gonna move these two lines

inside of our try block so press tab

here

and remove this blank line

now these two lines are part of our try

block right

so

after try we type accept

and then we add the type of the error

that our program may encounter

that is value error

okay

then we add a colon

and in this block we can define what

should happen if our program encounters

an error of type value error

in this case we want to print a proper

error message so print

invalid value

so we just try and accept we're telling

python hey go ahead and try running

these two lines of code if you encounter

an error of type value error then

instead of crashing the program

print this error message on the terminal

so this is how this works

now more accurately in programming terms

we refer to this kind of error as an

exception so an exception is a kind of

error that crashes our program so if the

user enters

an invalid value this line of code line

two will raise an exception and on line

four we'll catch it

and print this error message so our

program will no longer crash let me show

you so let's go ahead and run this

age 20

everything works just like before and

the exit code is zero beautiful let's

rerun this program and

enter asd

so we get this proper error message

invalid value and once again the exit

code is zero so that means our program

completed successfully didn't crash

now we can also handle different kinds

of errors or exceptions for example

right after we get the age

let's define a variable income and set

it to 20 000

and then define another variable called

risk and set it to income

divided by h

let's run this program and enter 0 as

the age to see what happens

so

0 is obviously a numerical value so when

we enter this value technically we

shouldn't get any exceptions

take a look

our program crashed with a zero division

error because we cannot divide the

number by zero once again look at the

exit code so we couldn't catch this kind

of error or this kind of exception

with this except block this except block

is only caching exceptions of type value

error and this happens when we try to

convert a non-numerical value to an

integer

so in a situation like this we should

handle different kinds of exceptions

we can add another accept statement for

an exception of type zero division error

now in this block we can print a

different kind of message

like age cannot be

zero

let's run our program one more time

now i'm going to enter 0 as the age

so we get this error message h can not

be 0 and look at the exit code

it's 0 so our program didn't crash

so to recap we used try except blocks to

handle exceptions that are raised in our

programs as a good programmer you should

always anticipate this kind of

exceptions and handle them properly

in this tutorial i'm going to talk to

you guys about comments in python we use

comments to add notes or comments to our

programs for example here i'm going to

make a print statement

sky is blue now before that

i can add a comment using a height sign

and then whatever i type here

it's going to get ignored it's not going

to get executed let me show you so let's

run this program

look we only see this message sky is

blue

so with this comment we can explain

something about our code we can use that

as reminders to fix things or clean

things up or we can use it to

communicate things with other developers

reading our code why we have written

this code in a certain way these are

good use cases for using comments we can

also have comments over multiple lines

so we can simply add more comments

each line should start with a new high

sign now one thing you need to avoid

when using comments is explaining what

the code does so here's an example of a

bad comment let me just delete these two

lines

and with this comment i'm going to say

print sky is blue

why is this a bad comment because it's

telling me the obvious it is obvious

that the next line is going to print sky

is blue now the problem with this

comment is that apart from being verbose

and repetitive if we come back here and

change sky to ocean

now this comment gets outdated so every

time we change this code then we'll have

to come back and modify the

corresponding comment so i've seen some

developers add comments in front of

their functions for example they define

a function let's say square that takes a

number and simply returns

number times number well it is obvious

that this function calculates and

returns the square of the given number

so there is really no need to add a

comment and explain that calculates

and returns the square of a number

this is very repetitive and it creates

noise in your code someone else reading

your code they get distracted with all

these unnecessary comments so use

comments to explain whys and how not

what's if you have made certain

assumptions you can use comments to

explain those assumptions or you can use

them to add notes to remind yourself or

other developers to do something in the

code

so comments are good but too much of a

good thing is a bad thing

in this tutorial i'm going to talk to

you guys about classes in python classes

are extremely important in programming

and they're not specific to python in

fact a lot of other programming

languages do support the notion of

classes we use classes to define new

types for example so far you have

learned about the basic types in python

like numbers strings and booleans these

are the basic or simple types in python

you also learn about a couple of complex

types like lists and dictionaries

while these types are extremely useful

they cannot always be used to model

complex concepts for example think of

the concept of a point or a shopping

cart a shopping cart is not a boolean

it's not a list it's not a dictionary

it's a different kind of thing so we can

use classes to define new types to model

real concepts

now in this tutorial i'm going to show

you how to define a new type called

point and this new type is going to have

methods for working with points for

example back to our main program let's

create a list numbers one two three

you know that here when we type dot we

get access to these functions or methods

available in list objects now similar to

this we're going to create a new type

called point this point is going to have

methods like move draw get distance from

another point these are the operations

that we can perform on points

so let me show you how to do this we

start by defining a class using the

class keyword and right after that we

give our class a name

now look at the naming convention i have

used here i've capitalized the first

letter here this is what we call pascal

naming convention so the convention we

use for naming our classes is different

from the convention we use for naming

our variables and functions

for variables and functions we always

use lowercase letters and we separate

multiple words using an underscore but

when naming classes we don't use an

underscore to separate multiple words

instead we capitalize the first letter

of every word so in this case our class

has only a single word if it had

multiple words let's say email client

look i've capitalized the first letter

of every word once again this is called

pascal naming convention and it comes

from the old pascal language that you

might have heard of

so

back to our point class

here we have a colon which means we're

going to define a block

now in this block we can define all the

functions or methods that belong to

points

for example we can define a function

called move for moving a point

now note that as soon as we type open

parenthesis pycharm automatically adds

self here this is a special keyword and

we're going to get back to this shortly

so

for now in this method let's print

move on the terminal

now let's define another method like

draw

so define draw

and in this method let's print draw on

the terminal

now let's remove the indentation

we're done with the definition of our

point class so we need to add two line

breaks

okay

so with this class we defined a new type

with this new type we can create new

objects so an object is an instance of a

class a class simply defines the

blueprint or the template for creating

objects and objects are the actual

instances based on that blueprint so we

could have tens or hundreds of points on

the screen these are the objects or the

instances

so to create an object we type out the

name of our class

and then call it like a function

this creates a new object and then

returns it so we can store that object

in a variable let's call that point one

there you go

now when we use the dot operator

look we have

these two methods that we defined draw

and move we also have a bunch of other

methods that start with two underscores

these are called magic methods we'll

look at them later in the course

so now let's call the draw method of our

point object and

run our program so you can see draw is

printed on the terminal

now apart from methods these objects can

also have attributes and these

attributes are like variables that

belong to a particular object for

example here

after we define point one

we can set point 1 dot x to 10 and point

1 dot y to 20.

now we can easily print out this

attributes let's print

0.1.x

and run our program one more time take a

look so the x coordinate of point one is

ten now we can create another object

let's call that point two

so point two

once again we type out the name of our

class and then call it like a function

now this object is completely different

from the first object so if we print

point 2 dot x

flow can we get this attribute error

because this point object doesn't have

an attribute called x

so each object is a different instance

of a point class

and here we can assign a value to point

two dot x

let's set that to one and then run our

program so we can see the x coordinate

of 0.2 is 1.

so to recap

we use classes to define new types

these types can have methods that we

define in the body of the class and they

can also have attributes that we can set

anywhere in our programs

you have learned how to create new types

using classes now there is a tiny

problem in this implementation

we can create a point object without an

x or y coordinates let me show you so

point

we create this object here and before we

set

point.x let's print point.x

run our program

we get this attribute error that you saw

in the last tutorial so point object has

no attribute called x

this is the problem we have here it is

possible to have a point object without

an x or y coordinates and that doesn't

really make sense because whenever we

talk about a point we need to know where

that point is located to solve this

problem we use a constructor a

constructor is a function that gets

called at the time of creating an object

so here on line 9 when creating this

point object we want to pass values for

x and y coordinates let's say 10

and 20 and with this this point object

that we get here will have its x and y

coordinates initialized so how do we do

this we need to add a special method in

this class called constructor

so on the top

we define a new function

look at the name of this function double

underscore

init double underscore

so init is short for initialize and this

is the function or the method that gets

called when we create a new point object

now press enter

so this automatically adds

self in parenthesis we're going to come

back to this shortly

now right after self we want to add two

extra parameters x and y so let's type

out x and y

and then in the body of this method we

should read the values passed here and

use them to initialize our object so

when we pass 10 and 20 these arguments

will be used for

x and y parameters

now to initialize our object we type out

code like this self dot x equals x

and then self.y equals y what is going

on here

this self that you see here is a

reference to the current object

so

back to line 13 when we create a new

point object self references that object

in memory the same object that we are

referencing using this variable

so earlier we typed point that x equals

10 with this code we set the x attribute

of this point object now what we have in

the constructor is exactly the same

we're using self to reference the

current object and then we set the x

attribute to the x argument passed to

this function

so using this init method we can

initialize our objects

and we refer to this method as a

constructor this method is used to

construct or create an object okay

so

now

let's remove line 14. so we create a

point object with these values and then

print point.x let's run our program

there you go x is 10. we can also change

these values later so just before

printing point.x we can set point.x to

11 and then run our program so x is

updated beautiful

all right here's an exercise for you i

want you to define a new type called

person

these personal objects should have a

name attribute as well as a talk

method

this is a very easy exercise so you can

tackle it in probably a couple of

minutes

all right so first we start with the

class keyword we define this person

class once again look at the naming

convention i have used here the first

letter of the first word in this case

the only word is uppercase

now in this class we define all the

methods that we need currently we have

only one method that is the talk method

so define talk

pycharm automatically adds self we come

back to this shortly

for now let's just print talk

so this is the body of our person class

we remove the indentation

and add two line breaks after defining

our classes

now we can create a personal object

let's call that john

we set it to person

we can call john.talk

let's run the program

so we get this message beautiful but our

personal objects should also have

a name attribute it doesn't make sense

to have a person without a name so that

is when we use the constructor function

so on the top we add a new method

the name of this method is double

underscore init double underscore

so we call this method a constructor

now in this method we need to add

another parameter that is name

so we simply set self.name to name

once again self references the current

object so we're setting the name

attribute of the current object to the

name argument passed to this method

with this we can go back to line nine

and when creating a personal object we

pass the name let's say john smith

now let's print john dot name

and run our program there you go so john

smith is printed on the terminal

beautiful so this is all you had to do

as part of this exercise but let's make

this program a little bit more

interesting

instead of printing this boring message

here let's print hi i am john smith

so we can use a formatted string with a

message like hi

i am now we want to dynamically add the

name of this person how do we do that

well look at the parameter

of this talk method as i told you before

every method in our class should have

this parameter self and this should be

the very first parameter of every method

okay so with itself we can get reference

to the current object

so

we can add curly braces and type out

self dot name

this returns the name attribute of the

current person object

with this we can remove

line 10

where we print john.name and simply call

john.talk

let's run our program

hi i am john smith beautiful

now we can create another personal

object let's say bob

it's a new person

called bob smith

when we say

bob.talk

and run our program

we get a different message hi i'm bob

smith so each object is a different

instance of a person class

in this tutorial i'm going to talk to

you guys about inheritance in python

inheritance is a mechanism for reusing

code and once again it's not limited to

python most languages that support

classes also support inheritance so let

me show you how it works let's say we

have this dot class with a simple walk

method in this method we're simply

printing the walk message on the

terminal now let's say in a real program

instead of just one line of code here

we're going to have 10 lines of code

now what if in the future we want to

define another class let's say cat

and we want to add this walk method

there as well we'll have to repeat all

that code in this new class

walk

this is bad because we have repeated or

duplicated our code in programming we

have a principle called dry which is

short for don't repeat yourself and

here's the reason

let's say sometime in the future we

discover a problem in our walk method if

we have repeated or duplicated this

method in many other places then we'll

have to come back and fix that problem

in every single place we have duplicated

this code so that's why in programming

we should not define something twice

so how can we solve this problem

well there are different approaches one

approach which is easier to understand

for beginners is inheritance and here's

how it works we define a new class

called mammal and move the walk method

right there

then we'll have the dog and cat classes

inherit that method from their parent

just like how humans inherit certain

attributes or behaviors from their

parents it's exactly the same

so

on the top we're defining a new class

let's call it mammal

then we need to move the walk method

there so we select it cut it using

command x on mac or control x on windows

and then paste it here

beautiful

now we want our dot class to inherit

this method from the mammal class so

right after the class name we add

parenthesis and then type out the name

of the parent class in this case mammal

that's all we had to do

so with this the dot class will inherit

all the methods defined in the mammal

class now there's a tiny problem here

if you look at line 9 there is a red

underline here

the reason this is happening is because

python doesn't like an empty class

so right now our dot class is empty it

doesn't have anything we either need to

add methods specific to dogs or just to

make python happy we can use the pass

statement and that basically means

nothing we're telling python interpreter

hey pass this line don't worry about it

but with this we don't have an empty

class okay

now as i told you before after each

class you should have two line breaks so

right now we only have one line break

and that is the reason we have this

little warning here so let's add another

black line beautiful

so our dog class is inheriting the walk

method from the mammal we need to apply

the same change to the cat class so

we'll have cat

inherit from mammal

and then

we use the pass statement here

with these changes now we can create

either a dog or a cat object let's say

dog one

we set it to a dog object

and when we type

dot look we have the walk method that is

defined in the mammal class we can

easily call it let's run our program

there you go we see the walk message

so both the dog and cat classes are

inheriting all the methods defined in

their parent class now here we can add

methods specific to dogs for example we

can define

a method called bark

and then print bark

now we don't need the pass statement

because we already defined one method in

our dog class

so now when we type out dog one dot

look we have two methods one is the walk

method that we inherited and the bark

method that we just defined in the dog

class similarly we can add a method

specific to a cat for example we can

define a method called be

annoying yeah i hate cats so

let's print

annoying

now when we create a cat object let's

remove that cat one

and type out cat one dot we have these

two methods walk and bnoy

so these are the basics of inheritance

in python now there is more to this that

really goes beyond the scope of this

beginner's tutorial if you're interested

to learn more about inheritance and

other mechanisms for reusing code i

encourage you to get my complete python

course

in this tutorial i'm going to talk to

you guys about modules in python a

module in python is basically a file

with some python code and we use modules

to organize our code into multiple files

just like sections and a supermarket

when you go to a supermarket there are

different sections for fruits vegetables

cleaning products and so on we don't

have one section with all the products

in the supermarket we have the same

concept in programming so instead of

writing all of our code instead of

writing all the functions and classes in

app.pi we want to break up our code into

multiple files we refer to each file as

a module with this not only is our code

better organized and structured but

we'll also have the ability to reuse our

code for example over here in app.pi

i've defined two functions for

converting weight from pounds to

kilograms and vice versa

now we can take these two functions and

put them in a separate module called

converters and then we can import that

module into any program that needs this

converter functions let me show you how

to do this so

let's open up our project panel and

right click the project

go to new and add a new file

we're going to call this file converters

dot pi

then we go back to app.pi

select all this code cut it and then

paste it into our new module

converters.pi

with this we have cleaned up our app

module it's not bloated with different

functions so as we write more functions

and classes we put them in their

corresponding modules

a module should contain all the related

functions and classes okay

now you want to import the converters

module into our app module and that is

really easy on the top right

import

converters

without the extension so we don't add

dot pi we only type out the name of the

file

let me close the project panel

now this converter is an object so we

can use the data operator to access its

members so currently we have defined

these two functions inside of our module

kilogram to pounds and pounds to

kilogram

so we can easily call one of these

functions let's pass 70 kilos get the

result and print it out

run our program

so

that is 155 pounds

now there is also another syntax for

importing modules let me show you so

instead of importing the entire module

we can import specific functions from

that module here's how it works we type

out from

then we add the name of our module so

converters

import now here if you press control and

space you can see the list of all the

functions defined in this module so here

we can grab one of these functions let's

say kilogram to pounds and with this we

can directly

call this function just like a function

defined in this file app.pi

compare what we have on line 4 with what

we have on line 6. on line 6 we'll have

to prefix this function call with the

name of an object converters so we have

to type converters dot and then we'll be

able to access this function

in contrast when we import a specific

function from our module then we can

easily call that function without

prefixing it with the module name so

here's what you need to take away we use

modules to better organize our code

instead of writing all the code instead

of writing all our functions in one file

we break up our code across multiple

files each file is called a module and

it should contain all the related

functions and classes

then we can import a module into another

module in this case we are importing the

converters module into our app module

and as you saw there are two ways to

import a module we can import the entire

module and then we'll get an object with

the same name as the module so we can

type converters dot and then we'll be

able to access all the functions and

classes defined in this module the other

approach is to import a specific

function or class from a module using

the from import statement

now here's your exercise earlier in the

course we had an exercise for finding

the largest number in the list

so here on the top we have a list of

numbers initially we set max for the

first number in this list

then we loop through this list get each

number

if the current number is greater than

max then we reset max and finally when

we're done with our loop we print max on

the terminal now here's what i wanted to

do this code currently has no

organization we don't have any functions

we don't have any modules we wrote all

the code in app.pi and that is okay for

small programs but as your programs grow

you need to properly organize your code

into functions classes and modules

so as part of this exercise i want you

to write a function call it find

max

this function should take a list and

return the largest number in that list

now after you do this go ahead and put

this function in a separate module so

extract it from here and put it in a

module called utils

so in this module we're going to have a

bunch of utility functions

okay

then

import the utils module into the current

module and call this function

finally get the result and print it on

the terminal this is a fantastic

exercise to teach you how to properly

organize your code so go ahead and spend

a couple of minutes on this exercise

so the first step is to define a

function called find max

so on the top i'm going to define a

function

find max

this function should take a list of

numbers so we add a parameter called

numbers

now instead of this function we want to

have these few lines this is the

algorithm for finding the largest number

in the list we don't want to bring the

first line because this is where we

create a list so somewhere in our

program we're going to create this list

and then pass it as an argument to find

max function okay so

let's go ahead and grab these few lines

cut them and

put them inside of find max function

all right so we find the largest number

in this list finally we need to return

it so

return

max

so here's our function now we need to

move this into a separate module so

let's go to the project panel

right click the project

and add a new file we can also add a new

python file is the same

let's call that utils

so if you add a new python file pycharm

automatically adds dot pi extension but

if you go to

new file we'll have to explicitly type

out dot pi

so make sure to get the extension right

now back to app.pi

let's cut this code and paste it into

this new module

okay beautiful

now we go back to app.pi and import our

new module we can either import the

entire module

so import utils and then access

individual functions so we can call

utils dot find max or we can explicitly

import this function from the utils

module it doesn't really make a

difference so

we could type from utils import

find max

and then

we don't need to prefix this with the

name of its object so we simply call

find max

now we need to call this after we

initialize our list

so first we need to define the list of

numbers

then

we pass that list as an argument to find

max we get the result which is max and

finally we print it on the terminal

let's go ahead and run our program

so the largest number in this list is

10. beautiful now one last thing before

we finish this tutorial

here we have this little warning under

max and the tooltip says shadows

built-in name max the reason we see this

is because in python we actually have a

function called max and it does the

exact same job as our find max function

so this is actually built into python

but i ask you to do it as an exercise

because it's a great exercise for

beginners now back to the warning

this warning is basically telling us

that we are overwriting the built-in max

function in python so we're changing the

meaning of this function and this is

considered a bad practice let me show

you what i mean so let's comment out

what we have on line four by putting a

heist line here we can also use

a shortcut command and slash on mac or

ctrl and slash on windows

so now this line is commented out look

at the color max here it's purple it's

the same color as print and this is the

color used to identify the built-in

functions

so now we can call this function

and give it

our list of numbers

run our program

we get the exact same result however

if we bring this line back once again we

can use the same shortcut that is

command and slash on mac or ctrl slash

on windows

now we are redefining max so up to this

line max used to be a function but after

line 4 is executed max is set to an

integer that is the largest number in

this list

so we'll no longer be able to call it

on line 5.

let's run our program and see what

happens

so there you go we get this type error

int object is not callable because max

is now an integer it's not a function so

we cannot call it

so to solve this problem we can rename

this variable to something else

so right click here

go to refactor

and rename

and rename this to maxi mum

so you can see the warning is gone

also we have the same warning in our

utils module

so here we're redefining max and as i

told you before this is a bad practice

we're changing the meaning of built-in

functions in python so

let's rename this as well i'm going to

use the shortcut that is shift and f6

there you go

and here we can change this to maximum

enter done

in this tutorial we're going to talk

about packages in python packages are

basically another way to organize our

code so currently we have only three

files or three modules in our project

but a real project can contain hundreds

or even thousands of modules we don't

want to add all those modules here

because over time this directory will

get bloated with so many files so a

better approach is to organize related

modules inside of a package so a package

is a container for multiple modules in

file system terms a package is a

directory or folder

so in our project we can add a new

directory and in that directory we can

add all the related modules as a

metaphor think of a mall when you go to

a mall or a shopping center there are

different sections for men's women's and

kids clothing so that is like a package

now when you go to the men's section

there are different areas for different

kinds of products we have a section for

shoes t-shirts jackets and so on so each

of these is like a module

so in this tutorial i'm going to show

you how to create and use packages in

python

here in our project panel right click

the project and add a new directory

let's call this directory

e

commerce

so we're going to create a package

called e-commerce and in this package

we're going to have all the modules

related for an e-commerce application

for example we can have modules for

sales shipping customer service and so

on so let's go ahead

now here we have an empty directory

in order to convert this to a package we

need to add a special file in it so

right click this directory and add

a new python file

call that file double underscore in it

double underscore

this is a special convention in python

when python interpreter sees

a file with this name in a directory it

treats this directory as a package we

also have a shortcut for that in pycharm

so let me delete this directory and

start again

so delete

once again right click the project

and go to new but instead of creating a

new directory we can create a new python

package

let's call our package ecommerce

as you can see pycharm automatically

creates this file for us so we don't

have to manually create it okay

now in this package let's add a new

module so a new python file

let's call it shipping

okay

now in this module we want to add a

function for calculating the shipping

cost

so define

calculate underline shipping

and don't worry about parameters or the

implementation we simply print

calculate underline shipping

now let's say we want to import this

shipping module into our app module

with this new structure the shipping

module is now part of the e-commerce

package so we cannot import it directly

we have to start from the e-commerce

package okay

so

back to app.pipe once again there are

two ways to import this module we can

import the entire module or we can

import one of its functions or classes

so let me show you both approaches first

we're going to import the entire module

import

now what is the name of our package that

is e-commerce right so e-commerce dot

shipping

so instead of typing import shipping we

type import e-commerce dot shipping we

have to prefix it with the name of its

package

now to access any of the functions or

classes in this module we'll have to

type out ecommerce.shipping

dot

and there you go now we can access the

calculate shipping function

so let's go ahead and run our program

we see this message printed on the

terminal beautiful however with this

approach every time you want to call one

of the functions in this module we'll

have to prefix it with e-commerce dot

shipping dot that is very verbose so

when working with packages we often use

the second approach using the from

statement

so we can type from

ecommerce.shipping

import

calculate shipping

now we don't have to prefix this

function with ecommerce.shipping

and we can call it multiple times in

this module so our code is a little bit

shorter but what if you want to use

multiple functions in the shipping

module

we can either import them all here so

calculate shipping

comma let's say calculate underline tags

or we can import the entire module and

then access all the functions or classes

in that module

so let me revert this back

to import the entire module we type from

e-commerce so we remove dot shipping

so from this package import

the shipping

module

now this shipping module is an object

so we can access

all the functions and classes defined

here using the dot operator so shipping

dot there you go calculate shipping

so to recap when using the from

statement we can either start from the

package and import a specific module

or we can start from package dot

module and then import a specific

function

like calculate shipping

so this was the basics of using packages

in python as i told you before packages

are extremely important especially when

you want to work with a framework like

django we use django for building web

applications with python and i'm going

to show you that later in this course

so in django we have quite a few

packages and each package contains

several modules so make sure to watch

the tutorials about modules and packages

one more time otherwise you're going to

get confused later when we get to django

in this tutorial i'm going to talk to

you guys about the built-in modules in

python so python comes with a standard

library that contains several modules

for common tasks such as sending emails

working with data and time generating

random values and passwords and so on

there are so many modules already built

into python and that means there is

already lots of functionality that we

can reuse we don't have to code all of

that from scratch let me show you where

you can find the standard library so

open up your browser and search for

python 3 module index

make sure to add the version number

because the modules in python 2 are

different from modules in python 3. so

here we search for python 3 module index

and the first page here you can see it's

python module index for python 3.

let's go ahead so these are all the

modules

built into python for example we have

modules for working with data and time

we have modules for sending emails for

encoding values there are so many

modules here now the explanation of all

this is beyond the scope of this course

that really requires its own course

because we have so many modules here but

don't let this list intimidate you this

is not something that you need to learn

right now as you work with python as you

build more applications gradually you'll

get more familiar with various modules

here in fact nobody knows all the

modules in python standard library

everybody knows some modules based on

the applications they have built

so in this tutorial i'm going to show

you how to use one of the built-in

modules for generating random values so

on the top we import

the random

module

now because random is a built-in module

we don't need to have a file here called

so python interpreter knows that random

is a built-in module and it knows where

to find it now if you're curious where

this random module is stored on the disk

let me show you so here in the project

panel

expand external libraries

then expand python 3

and then one more time python 3.7

library root

so this is a folder somewhere on your

computer in this folder we have all the

built-in modules in python so if you

scroll down

you should be able to find

the random module there you go it's

right here it's a random.pi you can open

this

and

this shows you the source code of this

module there you go

now in this tutorial we don't want to

worry about that so let's go back to our

app.pi and use this module to generate

random values

so when we import this module now we

have this object random so we can use

the dot operator to access its methods

one method that is very useful here is

the random method and every time we call

it it generates a random value between 0

to 1.

so here we can do a for loop

let's say four

i

in

range three so just to refresh our

memory we are using the range function

to create a range object we can loop

through this range object and in each

iteration this object will spit out a

value

so with this for loop we can execute

this code three times now let's indent

this okay and finally let's print the

result

there you go so we can see that in each

iteration we get a new random value

between 0 to 1. now what if we want a

random value for a particular age let's

say random values between 10 to 20. well

there is another method here around and

we passed two arguments here to specify

our range let's say 10 and 20.

run our program one more time

now we have the numbers 20 13 and 18. if

we run our program one more time we get

different values so 20 19 11 one more

time

look

we also have another powerful method for

randomly picking an item from a list

let's say we have a list of team members

and we want to randomly pick someone as

the leader let me show you how to do

that so we define the list of team

members

we set it to

john

mary

bob

and marsh

now

we can call random the choice

and pass

our members list

this method randomly picks an item from

this list and returns it so we can store

the result in leader and then print it

on the terminal

let's run our program

so now the leader is merry if we run our

program one more time this time it's

mosh now it's march again one more time

it really likes much

now it's bob you got the point so the

random module is very powerful and it

has a lot of applications

now here's a very cool exercise i wanted

to write this program to roll a dice so

every time we run this program we get

different values now we have three and

one next time we get three and six one

more time five and six four and three

double one that's a very cool exercise

so before we get started i want you to

pay attention to a few things

i want you to define a class called dice

in this class we're going to have a

method called roll

so every time we call this method we get

a tuple a tuple remember is a list of

values but that list cannot be changed

we cannot add a new item to it we cannot

remove it so it's like a read-only list

so every time we call the roll method we

should get a tuple of two random values

so go ahead and do this exercise you'll

see my solution next

all right we start by importing the

random module on the top

then we define a class called dice

colon in this class we want to have a

method called role so define role

parenthesis this automatically adds self

now in this method we want to generate

two random values between one to six so

we call

random

dot rand int

and pass one and six so this generates

the first number

we can put that here

now let's call this one more time so i'm

going to copy what we have on line five

put it here and change this variable to

second

so we have two variables first and

second with two random values finally we

need to return them in a tuple so return

parenthesis instead of square brackets

first and second

now in python when you want to return a

tuple from a function you don't have to

add this parenthesis so you can simplify

your code and python will automatically

interpret this as a tuple okay

so we're done with the definition of our

class we remove the indentation and add

two line breaks now we create an object

of this type so

we set dice to dice

next we roll the dice so dice.roll and

print the result on the terminal

that's all you have to do let's run this

program

so now we get two and five let's run it

one more time three and two one on one

beautiful

now we have this little warning here

that says expected to black lines found

one once again this is coming from pep8

pep is short for python enhancement

proposal we have so many python

enhancement proposals or peps pep8 is a

very famous one and in this document we

have

all the best practices for formatting

our code so pep8 says that after we

define our classes we should have two

line breaks we already done that so the

reason this is complaining is because we

have one line break before the class so

let's add one more line break now pie

charm is happy so basically pycharm is

following all the best practices defined

in pep 8.

now you don't have to memorize any of

these best practices as you code in

pycharm pycharm gives you little

warnings and gradually you will learn

how to properly format your code so it's

readable by other people

in this tutorial i'm going to show you

how to work with directories in python

so here on python 3 module index you can

see we have a module called pathlib

which provides an object oriented file

system patch that basically means it

provides classes that we can use to

create objects to work with directories

and files so if you click here you can

see how this module works you can see

all kinds of examples for example here

under basic usage you can see this is

how we import the past class from the

passlip module let me zoom in so you can

see clearly okay so look from passlip

that's our module import path note the

naming convention p is capitalized that

means path is a class

so we need to create an instance of this

class as you can see

right here

now there is so much documentation here

you can read this on your own but let me

quickly show you a few examples to help

you get started

so back in pycharm

on the top

from the passlip module let's import the

past class

now we need to create a path object to

reference a file or a directory on our

computer

so there are basically two ways to do

this we can use an absolute pass

or a relative path which basically means

a path starting from the current

directory for example if you want to

reference

this ecommerce directory in our project

we can use the relative path so we start

from the current directory and then go

somewhere else

with absolute paths we start from the

root of our hard disk

for example if you're on windows you

might have an absolute path like this c

drive backslash program

files

backslash microsoft so these are

directories

in c drive on windows we use a backslash

to build a path

if you're on mac or linux your paths

look a little bit different so instead

of a backslash we have a forward slash

let's say user

local slash bin

so these are examples of absolute paths

in this tutorial we're going to work

with a relative pass to work with this

ecommerce directory that we have in our

project now if you didn't create this

directory earlier simply right click on

the project and then go to new

directory

okay

so

let's close this panel

we create a path object

now if we don't pass an argument here

this will reference the current

directory

alternatively we can pass a string in

this string we can add a file or a

directory let's say the e-commerce

directory

now this returns a pass object so you

store it here

now this pass object has a few

interesting methods for example we can

check to see if a path exists by calling

the exist method this simply returns a

boolean so let's print it on the

terminal

there you go

so this path exists but if we change

this to let's say e-commerce 1 and run

our program we get false

we can also create a new directory for

example let's change this path to emails

now when we run this program obviously

we don't have this directory but we can

create it by calling the mkdir

method so make directory

let's run our program

all right this method returns none which

basically means it doesn't return any

values now if you look at the project

panel you can see here we have a new

directory called emails we can also

delete this directory so

instead of mkdir we call rm dir which is

short for remove directory

let's go ahead

now you can see that directory is gone

we can also find all the files and

directories in a given pass that is very

useful if you want to write a little

program to automate something for

example you can iterate over all the

spreadsheets in a directory open them

and process them

let me show you so first we change the

path

to the current directory

and then we call the glob method

with this method we can search for files

and directories in the current path so

as the first argument we need to pass a

string that defines a search pattern we

can type an asterisk and that means

everything all files and all directories

we can optionally add an extension

so to get all the files we use star dot

star

with this pattern we'll only get the

files in the current directory but not

the directories we can also search for

all the pi files or all the excel

spreadsheets anything

so let's search for all the pi files and

the current directory

now when we run our program

we get this generator object generator

objects are kind of an advanced topic

and they are beyond the scope of this

beginner's python course but for now all

you need to know is that we can iterate

or loop through these generator objects

so

instead of printing this generator

object let's just

iterate over it using a for loop so

for

file in

the generator object that is returned

from the glob method

let's print

file

run our program there you go

so these are all the pi files in my

current directory this could be

different on your machine if you didn't

follow the exercises i gave you earlier

for example this utils.pi we created

this as part of one of the exercises

earlier in this course so don't worry if

the files you see here are different on

your machine

so we can use the glob method to search

for files using a pattern we can also

get all the files and directories in the

current path

so we just use one asterisk

run our program take a look

so we have this ecommerce directory we

have notes.txt

this is a file i added earlier just to

write notes as part of my presentation

so you're not going to have this file

you also have a bunch of other

directories and files

even though python's standard library is

very comprehensive and has so many

modules for common tasks it's not

complete by any means that's why we have

this directory called python package

index or pypi and in this directory you

can find thousands of packages for doing

awesome things these are the packages

that people like you and i have built as

part of their projects and then they

published it in this directory for other

people to use so that's why we have a

fantastic community in python there are

so many python developers out there and

there's so many packages right in front

of us to reuse in our programs let's say

you want to send text messages in your

programs you don't have to build this

functionality from scratch you can

simply come to

pipi.org and search for

sms

as you can see there are so many

projects or packages that give you this

functionality of course not every

package not every project is complete or

bug-free some of them are still in

development or they have bugs but if you

look around i'm pretty sure for any kind

of functionality you can imagine there

is a good reliable and well-documented

package for you in my complete python

course i will show you some of the most

useful packages on pi pi for example you

will learn how to access the information

on yelp.com in your programs so you can

write your program and search for

businesses registered on yelp let's say

you want to search for the best barbers

in new york city i will show you how to

do that you also learn about the

technique called web scraping which

means you can build an engine and have

that engine browse a website

and extract information from html files

this is the same technique that google

does to index various websites so they

have several engines or web crawlers

these crawlers are continuously looking

at various websites and extracting

information from their pages when you

publish a blog post google's web crawler

finds the title of your post it's

keywords and so on so i'm going to show

you how to do that with python we'll

also look at browser automation and this

is extremely powerful because you can

automate testing of your web

applications so you might get a job as a

test engineer and your daily job is to

browse a website click here and there

fill out this form that form and ensure

that the website is functioning properly

you can automate all of that with a

powerful python package called selenium

as i've shown in my complete python

course

now in this tutorial i'm going to show

you how to install packages from

pipi.org

so here on pipi.org let's search for

open pi

xl this is a package that we use for

working with excel spreadsheets so let's

search for this package

there you go so currently it's at

version 2.5

on the top you can see this instruction

pip install open pi excel

this is the command that we need to type

into a terminal window to install this

package into our program

so back to pie chart here on the status

bar we can open up a terminal window for

executing various commands so let's open

it

now if you're on windows you're probably

going to see something different instead

of this dollar sign don't worry about

that just execute this command i'm going

to show you so pip

install open

pi excel make sure to spell everything

properly so pip is the tool that comes

with python installation and we use it

to install or uninstall packages

registered on

pipi.org so here we're using pip to

install this package open pi xl

enter let's go ahead with that it's

going to take a few seconds okay done

now we can import this package and its

modules just like the built-in modules

in python or the modules that we have in

our project

now if you're curious where this package

is stored on disk let me show you so

open up the project panel and then

expand external libraries

next expand python3

and then expand site packages this is

where all these packages that we

installed with pip are stored so here we

have open pi excel you can open this

in this folder we have another folder

called cell

now look what we have here we have this

init pi area i told you that whenever we

add this file to a folder python treats

that folder as a package so cell is a

package and in this package we have

these modules cell interface read-only

and text so as you can see this package

open pi excel has several sub packages

like cell chart chart sheet and so on

and in each package we have several

modules

in the next tutorial i will show you how

to work with excel files

so we have covered all the core concepts

in python i hope you learned a lot

please support my hard work by liking

this video and sharing it with others

and be sure to subscribe to my channel

for more tutorials like this

next we're going to work on our first

python project that involves automation

you're going to write a python program

that can process thousands of

spreadsheets in under a second are you

excited let's get started

in this tutorial i'm going to show you

something really awesome you can do with

python you're going to learn how to

process spreadsheets and this is

extremely valuable in situations where

you have hundreds or thousands of

spreadsheets that need to be updated if

you want to do this by hand it may take

hours days weeks or even months you can

simply build a python program in less

than half an hour and have that python

program automatically process thousands

of spreadsheets in under one second

so here we're going to work on this

excel spreadsheet you can download this

below this video in this spreadsheet we

have three columns transaction id

product id and price

now don't worry about the fourth column

yet so in a spreadsheet we record all

kinds of transactions but let's say due

to an error it could be a human error or

a system error the price that we have

here is wrong let's say we need to

decrease this by 10 percent if you want

to do this manually we'll have to come

back here

and add a formula so we type out equal

sign let's say we want to recalculate

the value of this cell that is c2 so

we'll have to get that and then multiply

it by

0.9 so that is like the 90

of the original price we are reducing

the price by 10

now when we hit enter you can see the

updated price

next we'll have to come back here select

the cell and then apply the same formula

to all the other rows now what if we

have thousands of rows here we'll have

to scroll up and down this is going to

be very tedious so we're going to write

a python program that will do this for

us it's going to automate this process

and not only that it will also

add this beautiful

chart

right here

once again if you want to open up

hundreds or thousands of spreadsheets

and add a chart to each one this is

going to take at least a week or two our

python program is going to do all of

this in a matter of seconds so let's get

started

all right the first thing i want you to

do is to download this transactions file

and add it to your project i'll put the

link below this video for you to

download

so if you're wondering how to put this

in this project you can simply right

click the project

and

if you're on mac you have this item

reveal in finder if you're on windows

you should see something like reveal in

explorer or file explorer or windows

explorer whatever it's called when you

click this

this opens up the directory on your

machine where this project is stored so

you can simply copy and paste the

transactions file right here

now here on the top first we need to

import the open pi excel package so

import open pi excel we can give it an

alias to make our code shorter so as

excel this is not required but it just

makes our code a little bit cleaner let

me show you so now instead of typing

open pi excel dot

we type x l dot okay so that's an alias

for this package

now in this package we have a function

for loading an excel workbook so let's

call load workbook

and

as the argument we pass transactions dot

xlsx

so this will load our excel workbook and

return a workbook object

okay

now if you open this workbook you can

see you have only one sheet and that is

called sheet one so to access that we

use square brackets

and specify the name of the sheet that

is sheet one make sure to spell this

with a capital s because this is case

sensitive if you don't split it properly

you're going to get an error

so this returns

our first sheet

now in this sheet we have various cells

so next you need to learn how to access

a particular cell and that is very easy

back to pycharm

with this sheet object we can use square

brackets and give the coordinate of a

cell

the coordinate is the combination of the

column and the row for example this cell

its coordinate is a one

so back to pycharm here we can type a1

and this returns

our first cell

there is also another approach to get a

cell instead of using square brackets

with a string

we can use

the cell method of the sheet object so

sheet that cell we pass the row and the

column so row one and column one

this returns the exact same cell

now let's print the value of the cell so

cell that value

and run our program

so the value is transaction id beautiful

so now we need to iterate over all these

rows and for each row we need to get the

value in the third column that is the

price we'll get that and then multiply

it by 0.9

so first we need to know how many rows

we have in this spreadsheet we can get

that from the sheet object so sheet

has

an attribute called max underline row

let's print this

so in this sheet we have four rows

and you can verify that here so we have

a total of four rows

so we need to add a for loop that would

generate the numbers one to four so

let's delete this print statement

and add a for loop for row in we're

going to use the range function to

generate a range of numbers

starting from 1

all the way to sheet dot max underline

row

plus one the reason we're adding one to

this is because as i told you before

this range function would generate

numbers starting from this value all the

way to this value but it will not

include the second value so currently

max row returns four if we use range of

one to four this would generate the

numbers one two and three but not four

so to include four we need to add one to

it

let's go back here

so we type sheet.max underline row plus

1.

now before going any further let's just

print row and make sure our program is

working up to this point

so

let's run this we get the numbers one to

four beautiful so now we can easily get

the cells in the third column however we

don't really want this first cell that's

the heading so technically we want to

ignore the first row

back here we want to change our range

function and start from two

okay

now

we're going to use sheet dot cell

to get access to the cell at this row

and the column should be three

we get a cell object let's print its

value and make sure

we're on the right track

so run our program

these are the values we get

5.95 6.95 and 7.95

these are the values in the third column

beautiful next we need to multiply each

value by 0.9

so instead of printing cell.value we

multiply it by 0.9 and this is the

corrected

underlying price

so this is the mistake we're going to

fix with our program

now we need to add a new cell to our

worksheet

so we want to add all the corrected

prices in a new column we could also

overwrite the values in this column but

in this tutorial i'm going to show you

how to add a new column

so using the same method now we need to

get a reference to the cell in the given

row but in the fourth column

so we call

sheet.cell and pass row and 4 as the

arguments

once again this returns a cell object

let's store that in a separate variable

and call it corrected

underline price underline cell

so note that my variable names are very

descriptive there is no guesswork

we have corrected price which holds the

actual value and we have corrected price

cell which is a sell object in this

spreadsheet

next we need to set the value for this

cell so we set corrected price sell dot

value to this corrected price

with these view lines we can easily

update our spreadsheet but first we need

to save it so

after our for loop we call workbook dot

save now let's save this in a new file

so we don't want to accidentally

overwrite the original file in case our

program has a bug

so i'm going to call that

transactions2.xlsx

now finally let's run our program

so you can see that happened in a split

of a second now here we have a new file

transactions2 when we open this we get

something like this so you can see we

have this fourth column with the updated

prices beautiful so half of the problem

is solved now we need to add a chart

here

to add a chart we need to import a

couple of classes on the top

so

after this import statement let's type

out from

open pi excel dot chart

import

bar chart

comma

reference

so let's see what's going on here

in this package we have a module called

chart and from this module we're

importing two classes bar chart and

reference again look at the naming

convention used here the first letter of

every word is capitalized

also it's better to add a line break

after our import statement to make our

code cleaner

so

before we save our workbook we need to

add a chart to the current sheet

first we need to select a range of

values for this exercise i'm going to

select the values in the fourth column

so all the values in rows 2 to 4. these

are the values i'm going to use in our

chart

now in this particular example it

doesn't really make sense to add a chart

per transaction but that doesn't really

matter we just want a bunch of numbers

to create a chart

so after our for loop we're going to use

the reference class to select a range of

values now the first argument in the

constructor is the sheet

so we pass our sheet here

then we add four keyword arguments the

first one is min underline row we set

this to two

the second one is max underline row we

set this to the maximum row in this

sheet that is sheet dot max underline

row so we want to select the cells in

row two

to four okay

now to make this code a little bit

cleaner i'm going to put this on a new

line so you can see clearly

now this is going to select all the

cells in all the columns in these rows

that's not what we want we only want the

values in the fourth column

so back here we need to set a couple

more keyword arguments min underline

call or column we set that to four and

also max underlying call we set that to

four as well

so we're limiting the range of cells

we're selecting to the fourth column

okay now

we're creating an instance of the

reference class let's store the result

in a variable called values so this

values object will have all these values

in the fourth column now we are ready to

create a chart

so we create an instance of the bar

chart class

and store it in this object

next we call chart that add underlying

data and pass our values

that is pretty straightforward finally

we need to add this chart to our sheet

so we call sheet that add underline

chart

and pass this chart object we should

also specify where we want to add this

chart

let's say we want to add it here on row

2 after the fourth column so the

coordinates of this cell is e 2 and this

is going to be the top left corner of

our chart

so as the coordinate i'm going to pass

e2 that's all we had to do done

let's run our program one more time

beautiful let's open up the updated

workbook

and here's the end result so right after

the fourth column we have this beautiful

chart now we could take this to the next

level we could add a legend here we

could change the color of these bars we

could even use a different kind of chart

it doesn't have to be a bar chart so to

learn more about this you can read the

documentation for open pi excel so our

program is complete but our code is

dirty it's not clean it's not organized

we don't have any functions here we have

written all the code in app.pi so let's

go ahead and organize this code like a

professional software developer

so on line four we're loading our

workbook then we're getting a reference

to the first sheet but we don't really

need these two lines here this was

purely for demonstration to show you how

you can access a cell so let's delete

these unnecessary lines this is a very

important practice as you're coding

always look at your code always review

it see if you have some code that is not

used always delete those

okay next we're iterating over all the

rows fixing the prices and then we

select these values to add a chart and

finally we save the workbook now if we

were going to use this to automate the

process of updating thousands of

spreadsheets this program wouldn't work

because it's only relying

on this file so we want to reorganize

this code and move it inside of a

function this function should take the

name of the file as an input so let's

define a function

let's call it process underline workbook

it gets a file name now we move all the

code inside of this function so let's

select everything

and then

press tab beautiful

now

back to our function

instead of loading this transactions

file we're going to load

this file name that's better

also now that our program is working

properly there is really no need to

store the result in a separate file so

here we can simply overwrite the same

file

so

let's pass file name

that is the end of our function

so now we have this reusable function we

can simply reuse this to process

thousands of spreadsheets

earlier in this python course you

learned how to find all the files in the

directory so you can get each file in a

directory and pass the name of the file

to this function this function will go

ahead and update that spreadsheet in

just a second or less

so that was just one example of using

python to automate repetitive boring

tasks that waste your time but

automation is not just about processing

excel spreadsheets there are so many

things we can automate here's a question

for you what do you want to automate how

do you want to use python to make your

life easier use the comment box below

and let me know i love to hear about

your ideas

next we're going to work on a project

that involves machine learning which is

a subset of artificial intelligence are

you excited let's get started

in this section you're going to learn

about machine learning which is a subset

of ai or artificial intelligence it's

one of the trending topics in the world

these days and it's going to have a lot

of applications in the future here's an

example imagine i ask you to write a

program to scan an image and tell if

it's a cat or a doc

if you want to build this program using

traditional programming techniques your

program is going to get overly complex

you will have to come up with lots of

rules to look for specific curves edges

and colors in an image to tell if it's a

cat or a dog but if i give you a black

and white photo your rules may not work

they may break then you'll have to

rewrite them or i might give you a

picture of a cat or a dog from a

different angle that you did not predict

before so solving this problem using

traditional programming techniques is

going to get overly complex or sometimes

impossible now to make the matter worse

what if in the future i ask you to

extend this program such that it

supports three kinds of animals cats

dogs and horses once again you'll have

to rewrite all those rules that's not

gonna work so machine learning is a

technique to solve these kind of

problems and this is how it works we

build a model or an engine and give it

lots and lots of data for example we

give you thousands or tens of thousands

of pictures of cats and dogs our model

will then find and learn patterns in the

input data so we can give it a new

picture of a cat that it hasn't seen

before and ask it is it a cat or a dog

or a horse and it will tell us with a

certain level of accuracy the more input

data we give it the more accurate our

model is going to be

so that was a very basic example but

machine learning has other applications

in self-driving cars robotics language

processing vision processing forecasting

things like stock market trends and the

weather games and so on so that's the

basic idea about machine learning next

we'll look at machine learning in action

a machine learning project involves a

number of steps the first step is to

import our data which often comes in the

form of a csv file we might have a

database with lots of data we can simply

export that data and store it in a csv

file for the purpose of our machine

learning project so we import our data

next we need to clean it and this

involves tasks such as removing

duplicated data if you have duplicates

in the data we don't want to feed this

to our model because otherwise our model

will learn bad patterns in the data and

it will produce the wrong result so we

should make sure that our input data is

in a good and clean shape if there are

data that is irrelevant we should remove

them if they are duplicated or

incomplete we can remove or modify them

if our data is text based like the name

of countries or genres of music or cats

and dogs we need to convert them to

numerical values so this step really

depends on the kind of data we are

working with every project is different

now that we have a clean data set we

need to split it into two segments one

for training our model and the other for

testing it to make sure that our model

produces the right result

for example if you have a thousand

pictures of cats and dogs we can reserve

eighty percent for training and the

other twenty percent for testing the

next step is to create a model and this

involves selecting an algorithm to

analyze the data there are so many

different machine learning algorithms

out there such as decision trees neural

networks and so on each algorithm has

pros and cons in terms of accuracy and

performance so the algorithm you choose

depends on the kind of problem you're

trying to solve and your input data now

the good news is that we don't have to

explicitly program an algorithm there

are libraries out there that provide

these algorithms one of the most popular

ones which we're going to look at in

this tutorial is scikit-learn

so we build a model using an algorithm

next we need to train our model so we

feed it our training data our model will

then look for the patterns in the data

so next we can ask it to make

predictions back to our example of cats

and dogs we can ask our model is this a

cat or a dog and our model will make a

prediction

now the prediction is not always

accurate in fact when you start out it's

very likely that your predictions are

inaccurate so we need to evaluate the

predictions and measure their accuracy

then we need to get back to our model

and either select a different algorithm

that is going to produce a more accurate

result for the kind of problem we're

trying to solve or fine-tune the

parameters of our model so each

algorithm has parameters that we can

modify to optimize the accuracy

so these are the high-level steps that

you follow in a machine learning project

next we'll look at the libraries and

tools for machine learning

in this lecture we're going to look at

the popular python libraries that we use

in machine learning projects the first

one is numpy which provides a

multi-dimensional array very very

popular library the second one is pandas

which is a data analysis library that

provides a concept called data frame a

data frame is a two-dimensional data

structure similar to an excel

spreadsheet so we have rows and columns

we can select data in a row or a column

or a range of rows and columns again

very very popular in machine learning

and data science projects

the third library is matplotlib which is

a two-dimensional plotting library for

creating graphs and plots

the next library is scikit-learn which

is one of the most popular machine

learning libraries that provides all

these common algorithms like decision

trees neural networks and so on

now when working with machine learning

projects we use an environment called

jupiter for writing our code technically

we can still use vs code or any other

code editors but these editors are not

ideal for machine learning projects

because we frequently need to inspect

the data and that is really hard in

environments like vs code and terminal

if you're working with a table of 10 or

20 columns visualizing this data in a

terminal window is really really

difficult and messy so that's why we use

jupiter it makes it really easy to

inspect our data

now to install jupiter we're going to

use a platform called anaconda so head

over to anaconda.com

download

on this page you can download anaconda

distribution for your operating system

so we have distributions for windows mac

and linux so let's go ahead and

install anaconda for python 3.7

download

all right so here's anaconda downloaded

on my machine let's double click this

all right first it's going to run a

program to determine if the software can

be installed so let's continue

and once again continue

continue pretty easy continue one more

time i agree with the license agreement

okay

you can use the default installation

location so don't worry about that just

click install

give it a few seconds now the beautiful

thing about anaconda is that it will

install jupyter as well as all those

popular data science libraries like

numpy pandas and so on so we don't have

to manually install this using

pip right now as part of the next step

anaconda is suggesting to install

microsoft vs code we already have this

on our machine so we don't have to

install it we can go with continue

and close the installation now finally

we can move this to trash because we

don't need this installer in the future

all right now open up a terminal window

and type jupyter

with a y space

notebook

this will start the notebook server on

your machine so enter

there you go this will start the

notebook server on your machine you can

see these default messages here don't

worry about them now it automatically

opens a browser window pointing to

localhost port 888

this is what we call jupiter dashboard

on this dashboard we have a few tabs the

first tab is the files tab and by

default this points to your home

directory so every user on your machine

has a home directory this is my home

directory on mac you can see here we

have a desktop folder as well as

documents downloads and so on on your

machine you're going to see different

folders so someone on your machine you

need to create a jupyter notebook i'm

going to go to desktop here's my desktop

i don't have anything here

and then

click new

i want to create a notebook for python

3. in this notebook we can write python

code and execute it line by line we can

easily visualize our data as you will

see over the next few videos so let's go

ahead with this

all right here's our first notebook we

can see by default it's called untitled

let's change that to

hello world so this is going to be the

hello world of our machine learning

project

let's rename this

now if you look at your desktop you can

see this file

helloworld.i pi

nb this is a jupyter notebook it's kind

of similar to our pi files where we

write our python code but it includes

additional data that jupiter uses to

execute our code

so back to our notebook

let's do

a print

hello world

and then click this run button here

and here's the result printed in jupiter

so we don't have to navigate back and

forth between the terminal window we can

see all the result right here

next i'm going to show you how to load a

data set from a csv file in jupyter

all right in this lecture we're going to

download a data set from a very popular

website called

gaggle is basically a place to do data

science projects so the first thing you

need to do is to create an account you

can sign up with facebook google or

using a custom email and password once

you sign up then come back here on

kaggle.com here in the search bar

search for

video game sales this is the name of a

very popular data set that we're going

to use in this lecture so

here in this list you can see the first

item with this kind of reddish icon so

let's go with that

as you can see this data set includes

the sales data for more than 16 000

video games

on this page you can see the description

of various columns in this data set we

have

rank name platform year and so on so

here's our data source it's a csv file

called vgsales.csv

as you can see there are over 16 000

rows and 11 columns in this data set

right below that you can see the first

few records of this data set so here's

our first record the ranking for this

game is one it's the wii sports game for

we as the platform and it was released

in year 2006

now what i want you to do

is to go ahead and download this data

set and as i told you before you need to

sign in before you can download this

so this will give you a zip file as you

can see here

here's our csv file now i want you to

put this right next to your jupiter

notebook on my machine that is on my

desktop so i'm going to drag and drop

this onto the desktop folder

now

if you look at the desktop you can see

here's my jupyter hello world notebook

and right next to that we have

vgsales.csv

with that

we go back to our jupiter notebook

let's remove the first line and instead

import

pandas

as pd with this we're importing pandas

module and renaming it to pd so we don't

have to type pandas. several times in

this code

now let's type pd dot

read underline csv

and

pass the name of our csv file that is vg

sales.csv now because this csv file is

in the current folder right next to our

jupyter notebook we can easily load it

otherwise we'll have to supply the full

path to this file so

this returns a data frame object which

is like an excel spreadsheet let me show

you so

we store it here

and then we can simply type df to

inspect it so one more time let's run

this program

here's our data frame with these rows

and columns so we have rank name

platform and so on

now this data frame object has lots of

attributes and methods that we're not

going to cover in this tutorial that's

really beyond the scope of what we're

going to do so i'll leave it up to you

to read panda's documentation or follow

other tutorials to learn about pandas

data frames but in this lecture i'm

going to show you some of the most

useful methods and attributes

the first one is shape

so shape let's run this one more time

so here's the shape of this data set we

have over 16 000 records and 11 columns

technically this is a two dimensional

array of 16 thousand and

okay

now you can see here we have another

segment for writing code so we don't

have to write all the code in the first

segment so here in the second segment we

can call one of the methods of the data

frame that is df dot describe

now when we run this program

we can see the output for each segment

right next to it so here's our first

segment here we have these three lines

and this is the output of the last line

below that we have our second segment

here we're calling the describe method

and right below that we have the output

of this segment so this is the beauty of

jupyter we can easily visualize our data

doing this with vs code and terminal

windows is really tedious and clunky so

what is this describe method returning

basically it's returning some basic

information about each column in this

data set so as you saw earlier we have

columns like rank year and so on

these are the columns with numerical

values now for each column we have the

count which is the number of records in

that column you can see our rank column

has 16

598 records whereas the year column has

16

327 records

so this shows that some of our records

don't have the value for the year column

we have null values so in a real data

science or machine learning project

we'll have to use some techniques to

clean up our data set one option is to

remove the records that don't have a

value for the year column or we can

assign them a default value that really

depends on the project now another

attribute for each column is mean so

this is the average of all the values

now in the case of the rank column this

value doesn't really matter but look at

the year

so the average year for all these video

games in our data set is 2006 and this

might be important in the problem we're

trying to solve

we also have standard deviation which is

a measure to quantify the amount of

variation in our set of values below

that we have min

as an example the minimum value for the

year column is 1980. so quite often when

we work with a new data set we call the

describe method to get some basic

statistics about our data

let me show you another useful attribute

so in the next segment let's type

df.values

let's run this

as you can see this returns a

two-dimensional array this square

bracket indicates the outer array

and the second one represents the inner

array so the first element in our outer

array is an array itself these are the

values in this array which basically

represent the first row in our data set

so the video game with ranking one which

is called wii sports

so this was a basic overview of pando's

data frames in the next lecture i'm

going to show you some of the useful

shortcuts of jupyter

in this lecture i'm going to show you

some of the most useful shortcuts in

jupyter

now the first thing i want you to pay

attention to is this green bar on the

left this indicates that this cell is

currently in the edit mode so we can

write code here

now

if we press the escape key

green turns to blue and that means this

cell is currently in the command mode so

basically the activated cell can be

either in the edit mode or the command

mode depending on the mode we have

different shortcuts so here we're

currently in the command mode

if we press h

we can see the list of all the keyboard

shortcuts

right above this list you can see

mac os modifier keys these are the extra

keys that we have on a mac keyboard if

you're a windows user you're not going

to see this so as an example here is the

shape of the command key this is control

this is option and so on

with this guideline you can easily

understand the shortcut associated with

each command let me show you

so here we have all the commands when a

cell is in the command mode for example

we have this command open the command

palette this is exactly like the command

palette that we have in vs code here's a

shortcut to execute this command that is

command shift and f

okay so here we have

lots of shortcuts of course you're not

going to use all of them all the time

but it's good to have a quick look here

to see what is available for you with

this shortcut you can write code much

faster so let me show you some of the

most useful ones

i'm going to close this

now

with our first cell

in the command mode i'm going to press b

and this inserts a new cell below this

cell

we can also go back to our first cell

press escape now the cell is in the

command mode we can insert an empty cell

above this cell by pressing a

so either a or b a for above and b for

below okay now if you don't want this

cell you can press d twice to delete it

like this

now in the cell i'm going to print a

hello world message so

print

hello world

now to run the code in this cell we can

click on the run button here

so

here's our print function and right

below that you can see the output of

this function but note that when you run

a cell this will only execute the code

in that cell in other words the code in

other cells will not be executed let me

show you what i mean so in the cell

below this cell i'm going to delete the

call to describe method

instead i'm going to print

ocean

now

i'm going to put the cursor back

in this cell where we print the hello

world message and run this cell

so we can see hello world is displayed

here

but the cell below is still displaying

the described table so we don't see the

changes here

now to solve this problem we can go to

the cell menu on the top and run all

cells together

this can work for small projects but

sometimes you're working with a large

data set so if you want to run all these

cells together it's going to take a lot

of time that is the reason jupiter saves

the output of itself so we don't have to

rerun that code if it hasn't changed

so this notebook file that we have here

includes our source code organized in

cells as well as the output for each

cell that is why it's different from a

regular pi file where we only have the

source code

here we also have auto completion and

intellisense so in the cell

let's call df dataframe

dot now if you press tab we can see all

the attributes and methods in this

object

so

let's call describe

now with the cursor on the name of the

method we can press shift and tab

to see this tooltip that describes what

this method does and what parameter it

takes so here in front of signature you

can see the described method these are

the parameters and their default value

and right below that you can see the

description of what this method does

in this case it generates descriptive

statistics that summarize the central

tendency and so on

similar to vs code we can also convert a

line to comment by pressing command and

slash on mac or control slash on windows

like this

now this line is a comment we can press

the same shortcut one more time

to remove the comment

so these were some of the most useful

shortcuts in jupyter now over the next

few lectures we're going to work on a

real machine learning project but before

we get there let's delete all the cells

here so we start with only a single

empty cell so here in this cell first

i'm going to press the escape button now

the cell is blue so we are in the

command mode and we can delete the cell

by pressing d twice

there you go now the next cell is

activated and it's in the command mode

so let's delete this as well

we have two more cells to delete there

you go

and the last one

like this

so now we have an empty notebook with a

single cell

over the next few lectures we're going

to work on a real machine learning

project imagine we have an online music

store

when our users sign up we ask their age

and gender and based on their profile we

recommend various music albums they're

likely to buy so in this project we want

to use machine learning to increase

sales

so we want to build a model we feed this

model with some sample data based on the

existing users our model will learn the

patterns in our data so we can ask it to

make predictions when a new user signs

up we tell our model hey we have a new

user with this profile what is the kind

of music that this user is interested in

our model will say jazz or hip hop or

whatever and based on that we can make

suggestions to the user

so this is the problem we're going to

solve

now back to the list of steps in a

machine learning project

first we need to import our data then we

should prepare or clean it next we

select a machine learning algorithm to

build a model we train our model and ask

it to make predictions and finally we

evaluate our algorithm to see its

accuracy if it's not accurate we either

fine tune our model or select a

different algorithm so let's focus on

the first step head over to bit.li

music csv this is a very basic csv that

i've created for this project it's just

some random made-up data it's not real

so we have a table with three columns

age

gender and genre gender can either be

one which represents a male or zero

which represents a female here i'm

making a few assumptions i'm assuming

that men between 20 and 25 like hip-hop

men between 26 and 30 like jazz and

after the age of 30 they like classical

music

for women i'm assuming that if they're

between 20 and 25 they like dance music

if they're between 26 and 30 they like

acoustic music and just like men after

the age of 30 they like classical music

once again this is a made-up pattern

it's not the representation of the

reality

so let's go ahead and download this csv

click on this dot dot icon here and

download this file

in my downloads folder here we have this

music.csv

i'm going to drag and drop this onto

desktop because that's where i've stored

this hello world notebook so i want you

to put the csv file right next to your

jupyter notebook

now back to our notebook we need to read

the csv file so just like before first

we need to import the pandas module so

import pandas as pd

and then we'll call pd that read

underline csv

and the name of our file is music.csv

as you saw earlier this returns a data

frame which is a two-dimensional array

similar to an excel spreadsheet so let's

call that music

underline data

now let's inspect this music underline

data to make sure we loaded everything

properly so run

so here's our data frame beautiful next

we need to prepare or clean the data and

that's the topic for the next lecture

the second step in a machine learning

project is cleaning or preparing the

data and that involves tasks such as

removing duplicates null values and so

on now in this particular data set we

don't have to do any kind of cleaning

because we don't have any duplicates and

as you can see all rows have values for

all columns so we don't have null values

but there is one thing we need to do

we should split this data set into two

separate data sets

one with the first two columns which we

refer to as the input set and the other

with the last column which we refer to

as the output set so when we train a

model we give it two separate data sets

the input set and the output set the

output set which is in this case the

genre column contains the predictions so

we're telling our model that if we have

a user who's 20 years old and is a male

they like hip hop

once we train our model then we give it

a new input set for example we say hey

we have a new user who is 21 years old

and is a male what is the genre of the

music that this user probably likes as

you can see in our input set we don't

have a sample for a 21 year old male so

we're going to ask our model to predict

that

that is the reason we need to split this

data set into two separate sets input

and output

so back to our code

this data frame object has a method

called drop

now

if you put the cursor under method name

and press shift and tab

you can see this tooltip so this is the

signature of this drop method these are

the parameters that we can pass here

the parameter we're going to use in this

lecture is columns which is set to none

by default with this parameter we can

specify the columns we want to drop

so

in this case we set columns

to an array with one string genre

now this method doesn't actually modify

the original data set in fact it will

create a new data set but without this

column

so

by convention we use a capital x to

represent that data set so capital x

equals this expression

now

let's inspect x

so as you can see our input set or x

includes these two columns age and

gender it doesn't have the output or

predictions

next we need to create our output set

so

once again we start with our data frame

music data

using square brackets we can get all the

values in a given column in this case

genre

once again this returns a new data set

by convention we use a lowercase y to

represent that so that is our output

data set

let's inspect that as well

so

in this data set we only have the

predictions or the answers

so we have prepared our data next we

need to create a model using an

algorithm

the next step is to build a model using

a machine learning algorithm there are

so many algorithms out there and each

algorithm has its pros and cons in terms

of the performance and accuracy in this

lecture we're going to use a very simple

algorithm called decision tree now the

good news is that we don't have to

explicitly program these algorithms

they're already implemented for us in a

library called scikit-learn

so

here on the top

from sklearn.3

let's import the decision

tree

classifier

so sklearn is the package that comes

with scikit-learn library this is the

most popular machine learning library in

python

in this package we have a module called

tree and in this module we have a class

called decision tree classifier this

class implements the decision tree

algorithm okay

so

now we need to create a new instance of

this class

so

at the end let's create an object called

model and set it to a new instance of

decision

tree

classifier

like this

so now we have a model next we need to

train it so it learns patterns in the

data and that is pretty easy we call

model

that fit

this method takes two data sets the

input set and the output set

so

they are capital x and y

and finally we need to ask our model to

make a prediction so we can ask it what

is the kind of music that a 21 year old

male likes now before we do that let's

temporarily

inspect our initial data set that is

music data

so

look what we got here

as i told you earlier i've assumed that

men between 20 and 25 like hip-hop music

but here we only have three samples for

men aged 20

23 and 25. we don't have a sample for a

21 year old male so if you ask our model

to predict the kind of music that a 21

year old male likes we expect it to say

hip hop

similarly

i've assumed that women between 20 and

25 like dance music but we don't have a

sample for a 22 year old female so once

again if you ask our model to predict

the kind of music that a 22 year old

woman likes we expect it to say dance

so

with these assumptions let's go ahead

and ask our model to make predictions

so

let's remove the last line

and instead we're going to call model

dot predict

this method takes a two dimensional

array so here's the outer array in this

array each element is an array so i'm

going to pass another array here and in

this array i'm going to pass a new input

set a 21 year old male so 21 comma 1.

that is like a new record

in this table

okay so this is one input set let's pass

another input set for a 22-year female

so here's another array

here we add 22 comma zero

so we're asking our model to make two

predictions at the same time

we get the result and store it

in a variable called predictions and

finally let's inspect that

in our notebook

run look what we got

our model is saying that a 21 year old

male likes hip hop and a 22 year old

female likes dance music

so our model could successfully make

predictions here beautiful but wait a

second building a model that makes

predictions accurately is not always

that easy as i told you earlier after we

build a model we need to measure its

accuracy and if it's not accurate enough

we should either fine-tune it or build

the model using a different algorithm so

in the next lecture i'm going to show

you how to measure the accuracy of a

model

in this lecture i'm going to show you

how to measure the accuracy of your

models now in order to do so first we

need to split our data set into two sets

one for training and the other for

testing because right now we're passing

the entire data set for training the

model and we're using two samples for

making predictions that is not enough to

calculate the accuracy of a model a

general rule of thumb is to allocate 70

to 80 percent of our data for training

and the other 20 to 30 percent for

testing then instead of passing only two

samples for making predictions we can

pass the data set we have for testing

we'll get the predictions and then we

can compare these predictions with the

actual values in the test set based on

that we can calculate the accuracy

that's really easy all we have to do is

to import a couple of functions and call

them in this code let me show you so

first on the top

from sklearn

that model underline selection module we

import a function called train test

split with this function we can easily

split our data set into two sets for

training and testing

now right here after we define x and y

sets we call this function

so

train

test split

we give it three arguments x

y and a keyword argument that specifies

the size of our test data set so test

underline size we set it to 0.2 so we

are allocating 20 of our data for

testing

now this function returns a tuple so we

can unpack it into four variables right

here x underline train

x underline test

y underline train

and y underline test

so the first two variables are the input

sets for training and testing and the

other

are the output sets for training and

testing

now

when training our model

instead of passing the entire data set

we want to pass only the training data

set so

x

underline train

and y

underline train

also when making predictions instead of

passing these two samples we pass

x underline test

so that is the data set that contains

input values for testing

now we get the predictions to calculate

the accuracy we simply have to compare

these predictions with the actual values

we have in our output set for testing

that is very easy first on the top we

need to import a function

so from sklearn that metrics

import

accuracy

underlying score

now at the very end we call this

function so accuracy score

and

give it two arguments y underline test

which contains the expected values and

predictions

which contains the actual values

now this function returns an accuracy

score between 0 to 1. so we can store it

here

and simply display it on the console

so let's go ahead and run this program

so the accuracy score is one or a

hundred percent but if we run this one

more time we're going to see a different

result because every time we split our

data set into training and test sets

will have different data sets because

this function randomly picks data for

training and testing

let me show you so put the cursor in the

cell now you can see this cell is

activated note that if you click this

button here it will run this cell and

also insert a new cell below this cell

let me show you so if i go to the second

cell

press escape button

now we are in the command mode press d

twice

okay now it's deleted

if we click the run button

you can see this code was executed and

now we have a new cell

so if you want to run our first cell

multiple times every time we have to

click this and then run it and then

click again and run it it's a little bit

tedious so i'll show you a shortcut

activate the first cell

and press ctrl and enter

this runs the current cell without

adding a new cell below it so back here

let's try it multiple times okay now

look the accuracy dropped to 0.75 it's

still good so the accuracy score here is

somewhere between 75 percent to 100

but let me show you something

if i change the test size from 0.2

to 0.8 so essentially we're using only

20 of our data for training this model

and we're using the other 80

for testing now let's see what happens

when we run this cell multiple times so

control and enter

look the accuracy immediately dropped to

0.4 one more time

now 46 percent 40

26

it's really really bad

the reason this is happening is because

we are using very little data for

training this model this is one of the

key concepts in machine learning the

more data we give to our model and the

cleaner the data is we get the better

result so if you have duplicates

irrelevant data or incomplete values our

model will learn bad patterns in our

data that is why it's really important

to clean our data before training our

model

now let's change this back to 0.2

run this one more time

okay now the accuracy is one

seventy-five percent

now we drop to fifty percent again the

reason this is happening is because we

don't have enough data some machine

learning problems require thousands or

even millions of samples to train a

model the more complex the problem is

the more data we need for example here

we're only dealing with a table of three

columns but if you want to build a model

to tell if a picture is a cat or a dog

or a horse or a lion we'll need millions

of pictures the more animals we want to

support the more pictures we need in the

next lecture we're going to talk about

model persistence

so this is a very basic implementation

of building and training a model to make

predictions

now to simplify things i have removed

all the code that we wrote in the last

lecture for calculating the accuracy

because in this lecture we're going to

focus on a different topic

so basically

we import our data set

create a model

train it and then ask it to make

predictions

now this piece of code that you see here

is not what we want to run every time we

have a new user or every time we want to

make recommendations to an existing user

because training a model can sometimes

be really time consuming in this example

we're dealing with a very small data set

that has only 20 records but in real

applications we might have a data set

with thousands or millions of samples

training a model for that might take

seconds minutes or even hours so that is

why model persistence is important once

in a while we build and train our model

and then we'll save it to a file now

next time we want to make predictions we

simply load the model from the file and

ask it to make predictions that model is

already trained we don't need to retrain

it it's like an intelligent person so

let me show you how to do this it's very

very easy

on the top from

sklearn.externals

module

we import

joblib

this joblib object has methods for

saving and loading models

so

after we train our model we simply call

joblib.dump

and give it to arguments

our model

and the name of the file in which we

want to store this model

let's call that music

dash recommender

dot

job lib

that's all we have to do now temporarily

i'm going to comment out this line we

don't want to make any predictions we

just want to store our trained model in

a file so

let's run the cell with control and

slash

okay

look

in the output we have an array that

contains the name of our model file so

this is the return value of the dump

method

now back to our desktop right next to my

notebook you can see our job live file

this is where our model is stored it's

simply a binary file

now back to our jupyter notebook as i

told you before in a real application we

don't want to train a model every time

so

let's comment out these few lines so

i've selected these few lines on mac we

can press command and slash on windows

control slash

okay these lines are commented out now

this time instead of dumping our model

we're going to load it so we call the

load method

we don't have the model we simply pass

the name of our model file this returns

our trained model

now with these two lines we can simply

make predictions so

earlier we assumed that men between 20

and 25 like hip-hop music

let's print predictions and see if our

model is behaving correctly or not

so ctrl and enter there you go

so this is how we persist and load

models

earlier in this section i told you that

decision trees are the easiest to

understand and that's why we started

machine learning with decision trees in

this lecture we're going to export our

model in a visual format so you will see

how this model makes predictions that is

really really cool let me show you

so

once again i've simplified this code so

we simply import our data set

create

input and output sets

create a model and train it that's all

we are doing

now i want you to follow along with me

type everything exactly as i show you in

this lecture don't worry about what

everything means we're going to come

back to it shortly

so on the top

from sklearn

import tree

this object has a method for exporting

our decision tree in a graphical format

so after we train our model

let's call tree

dot export underline graph viz

now here are a few arguments we need to

pass the first argument is our model

the second is the name of the output

file so here we're going to use keyword

arguments because this method takes so

many parameters and we want to

selectively pass keyword arguments

without worrying about their order

so

the parameter we're going to set is out

underline file

let's set this to

music dash recommender

dot dot this is the dot format which is

a graph description language you'll see

that shortly

the other parameter we want to set

is feature underline names we set this

to an array of two strings

age

and gender these are the features or the

columns of our data set so they are the

properties or features of our data okay

the other parameter

is class names so class underline names

we should set this to the list of

classes or labels we have in our output

data set like hip hop jazz classical and

so on

so this white data set includes all the

genres or all the classes of our data

but they're repeated a few times in this

data set so

here we call y dot unique

this returns the unique list of classes

now we should sort this alphabetically

so we call the sorted function

and pass the result a y dot unique

the next parameter

is label

we set this to a string all

once again don't worry about the details

of these parameters we're going to come

back to this shortly so set label to all

then round it

to true and finally

filled to true

so this is the end result

now let's run this cell using ctrl and

enter

okay

here we have a new file music

recommender dot dot that's a little bit

funny so we want to open this file with

vs code so drag and drop this into a vs

code window

okay here is a dot format it's a textual

language for describing graphs

now to visualize this graph we need to

install an extension in vs code so on

the left side click the extensions panel

and search for dot d o t

look at the second extension here

graphviz or dot language

by staphon vs

go ahead and install this extension and

then reload vs code once you do that you

can visualize this dot file so let me

close this tab

all right

look at this dot dot here on the right

side click this you should have a new

menu open preview to the site so click

that

all right here's the visualization of

our decision tree let's close the dot

file

there you go this is exactly how our

model makes predictions so we have this

binary tree which means every node can

have a maximum of two children on top of

each node we have a condition if this

condition is true we go to the child

node on the left side otherwise we go to

the child node on the right side so

let's see what's happening here

the first condition is age less than or

equal to 30.5 if this condition is false

that means that user is 30 years or

older so the genre of the music that

they're interested in is classical

so here we're classifying people based

on their profile that is the reason we

have the word class here so a user who

is 30 years or older belongs to the

class of classical

or people who like classical music

now what if this condition is true that

means that user is younger than 30. so

now we check the gender

if it's less than 0.5 which basically

means if it equals to zero then we're

dealing with a female so we go to the

child node here

now once again we have another condition

so we're dealing with a female who is

younger than 30. once again we need to

check their age so is the age less than

25.5 if that's the case then that user

likes dance music otherwise they like

acoustic music

so this is the decision tree that our

model uses to make predictions now if

you're wondering why we have these

floating point numbers like

25.5 these are basically the rules that

our model generates based on the

patterns that it finds in our data set

as we give our model more data these

rules will change so they're not always

the same also the more columns or more

features we have our decision tree is

going to get more complex currently we

have only two features age and gender

now back to our code let me quickly

explain the meaning of all these

parameters we set fill to true so each

box or each node is filled with a color

we set rounded to true

so they have rounded corners

we set label to all

so every node has labels that we can

read

we set class names to the unique list of

genres and that's for displaying the

class for each node right here

and we set feature names to age and

gender so we can see the rules in our

notes

so that was a short and sweet

introduction to machine learning now you

can use the materials that you learned

in this section and apply them to solve

a different sort of problems now here's

a question for you what ideas do you

have for machine learning what kind of

problems do you want to solve with

machine learning use the comment box

below and let me know i love to hear

about your ideas

next we're going to use python and a

popular framework called django to build

a web application are you ready let's

get started

in this tutorial i'm going to show you

how to create your first website with

python at a very popular framework

called django so it's spelled with a

silent d and it's pronounced django it's

a web framework for perfectionists with

deadlines so if you're a perfectionist

and you want to quickly put together a

website that is fast scalable and secure

django is your best friend

and here are the popular websites built

with django like instagram spotify

youtube washington post and so on now

you might ask what is a framework and

why do we need a framework to build a

web application or a website

well a framework is essentially a

library of reusable modules these

modules provide functionality for common

tasks for example in case of a web

framework like django we have modules to

work with http requests urls sessions

cookies and so on these are the concerns

of pretty much every website or web

application out there so all this

functionality is already baked into

django we don't have to code it from

scratch that is why we use a framework

like django

now technically a framework is more than

a library so apart from providing these

modules it also defines a structure for

our application it tells us what folders

and files we should have in our project

so this provides a consistency amongst

various django projects so as you move

from one company to another and work on

different projects you can easily

transition from one project to another

because all these applications follow

the same structure

now with that introduction let's create

our first django project

so back to pycharm close the hello world

project and create a new project

okay let's call this new project pi

shop

go ahead

all right now down the bottom

let's open up a terminal window

in this window we're going to install

django so we use pip to install django

but be sure to add two equal signs here

followed by 2.1 with this we're telling

pip that we want to install django

version 2.1 the reason i'm doing this is

because in the future when you're

watching this video chances are there is

a newer version of django out there i

want to make sure that you can easily

follow these tutorials even though what

i'm going to show you in these tutorials

will most likely work with the latest

version of django i just want to be on

the safe side so let's go ahead with

this

all right django is installed next we

need to create a django project so here

press ctrl and l this cleans up our

terminal window you don't have to do it

but it's just easier to see

to create a django project we need to

execute this command django

dash admin

space start

project

space

we're going to call this project pi

shop

space period

so when we install django django brings

a command line utility called django

admin so this is a utility or program

that we can execute from the command

line or terminal right here

now this program takes various arguments

in this case we want to use this

argument start project with this we're

going to create a project called pi shop

in the current folder so this period is

important here that means the current

folder

if you don't add this period this

utility is going to create an extra

folder and that looks a little bit

repetitive so let's go ahead with this

all right

now back to the project panel if you

expand pi shop

you can see that this is our project

that we created in pycharm and in this

folder we have

these files

so in it that pi you have seen this

before that means this folder is a

package so we can import various modules

from this package into other modules so

here we have the settings module in this

module we defined various settings for

our application you're going to see this

later in this course we also have the

urls module and with this module we

define what should the user see when

they go to let's say slash about slash

contact slash products

shopping cart again we're going to work

with this zone and finally we have this

module ws gi that is short for web

server gateway interface the purpose of

this module is to provide a standard

interface between applications built

with django and web servers this is an

advanced topic so for now don't worry

about it

the outside of this folder we also have

this new file in our project that is

manage.pi

as the name implies we use this module

to manage this django project with this

we can start our web server we can work

with our database again we're going to

work with this soon

so let's open up the terminal window one

more time

now type out this command python if

you're on windows or python 3 if you're

on mac because as i told you at the

beginning of the course mac by default

comes with an installation of python

that is python 2. but in this course

we're using python 3. so python 3 space

manage dot pi

space

run server

what is going on here so with python

interpreter we are running this program

manage.pi and passing run server as an

argument this manage.pi is essentially

the same program that we worked with

here django admin

but we use django admin before creating

a django project now we have a django

project so in this project we work with

manage.pipe this is a module that

contains some python code so we use this

module to manage our django project

so let's go ahead and run our

development web server

as you can see this started a

development web server at this address

http colon forward slash forward slash

127.0 0.0.1 that is the address of your

current machine now note that after this

we have colon 8000 unfortunately the

link below this address has a problem as

you can see the port is excluded so if

we click this

it opens up our web browser and points

it to this address so we don't have the

port number let's add colon 8000 at the

end and here's our first django website

so we created this django project

now this django project can contain

multiple apps these apps don't represent

the entire application there are small

functional areas in our django project

here's an example imagine you want to

build a website or a web application

like amazon amazon is a big website it

has so many different functions instead

of implementing all these functions in a

django project we divide this project

into small functional areas that are

focused on one concern for example we

could have functional areas like product

management order management customer

management these are completely

different functional areas the functions

we have for managing the customers are

different from the functions for

managing the products by the same token

when you go to an organization there are

small departments or small offices

specializing in different areas so with

this analogy we divide the django

project into multiple django apps each

app is focused on one functional area

so in this tutorial i'm going to show

you how to add a new app to manage the

products in our imaginary shop in the

future let's say we want to add a blog

to our online shop we could come back

here and create a new app that

represents a blog now the beauty of

these apps is that we can reuse them

across different django projects because

each app is essentially a python package

let me show you so back to our project

let's open up a terminal window

so this is the terminal window we opened

earlier where we started our web server

now up here we have this plus button for

creating a new terminal window so let's

click that

now let's type out this command python

on windows or python 3 on mac

manage dot pi so we're using the same

program the same module but this time

with a different argument start app

and we're going to call that app

products

let's go ahead all right now

here we have a new folder called

products

let's see what we have in this folder we

have a subfolder called migrations we'll

look at this later below that we have

this init.pi so products is a package we

can take this package and reuse it in

another django application or more

specifically django project we can also

publish this package to pi pi for other

people to reuse in their django projects

for example if someone else wants to

build an online shop they can reuse this

package for managing the list of

products they don't have to build this

functionality from scratch okay we have

this module admin and this is used for

defining how the administrative panel of

this app will look like again we're

going to come back to this later

below that we have this module apps

unfortunately the name is a little bit

confusing because right now we are

inside of one app that is the products

app and it doesn't make sense to have a

module called apps inside of an app so i

don't know why django creators decided

to call this module apps but basically

we use this module to store various

configuration settings for this app so

it would be better to call this config

but that aside let's move on

next we have models and this is where we

define classes or new types for modeling

the concepts in this app in this domain

for example in the domain of products

you probably have concepts like product

category review and so on so we could

model these concepts using classes again

we're going to come back to this and

define a new class here

next we have tests.pi and this is where

we write automated tests for this app

that's an advanced topic beyond the

scope of this course so don't worry

about it and finally we have the views

module and this is where we define what

should the user see when they navigate

to a certain page

in this tutorial i'm going to show you

how to create your first view or view

function in django what is the view

function a view function is basically a

function that gets called by django when

the user navigates to a particular page

for example here we are on the home page

of our website

when we go to slash products our browser

sends an http request to our web server

at this point django takes that request

it inspects the url or the address it

figures out that we want to see the list

of products then it will call a function

which we call a view function and the

job of this function is to return the

response to the browser or to the client

so this function should generate some

html markup to be returned to the client

our browser will get this html content

and display it as a page right here

now technically if you want to be a web

developer you need to know html css and

javascript i'll try to do my best to

hold your hand throughout this course

but in the future be sure to watch a

tutorial about html css and javascript

on my channel i have plenty of

javascript tutorials i recommend you to

start with my javascript tutorial for

beginners

so back to our project

inside the products app let's open up

the views module

so here on the top we have some

boilerplate code from django.shortcuts

we are importing the render function so

django is a package shortcuts is a

module and we are importing the render

function you will see this soon below

that we have this comment we don't need

it let's create our first view function

so define we call this function index it

doesn't really matter but by convention

we use the word index for the main page

of an app

so when we go to slash products this

will be the main page of our products

app now potentially in the future we

could support additional urls inside of

this app for example products slash new

or training and so on

so we call this function index

now all our view functions should always

take a parameter and

that is the http request that is passed

to this view function

so as i told you before when we navigate

to slash products our browser sends an

http request to our web server django

takes this request and sends it to our

view function

with this request object we can find

information about the client

now in this tutorial we don't want to

worry about html we just want to return

some plain text to the browser like

hello world so on the top

from django.httpmodule

we need to import a class called http

response

with this class we can create an http

response to return to the client or the

browser so back to our view function

here we return an http response object

so we're creating an instance of this

class right

now as an argument to the constructor we

pass hello world

now we need to add an extra blank line

above the index function to make python

happy beautiful

as simple as that

so we are done with this view function

but nowhere django knows that it should

call this function when we send a

request to slash products

so we need to tell django that hey

whenever there is a request to slash

products call this index function we

need to map this url to this function

a url is short for uniform

resource locator and that basically

means address

okay

so let's do the mapping we're done with

this module close it

back to our products app right click

this folder and add a new python file

call that urls the name is very

important here this is one of the

conventions that django framework

defines so we need to follow this

convention to structure our project

okay so this adds urls.pi inside of the

products app now in this module once

again by convention we should define a

variable called url patterns

make sure to spell it exactly as you see

here so there is no underscore between

these two words and all characters are

in lower case

so we set this to a list object

in this list we map various urls to

their view functions

now to reference a url we need to import

the path function

so on the top

from

django.urls let's import the path

function

with this function we can map a url to a

view function so we call the path

function

the first argument is a string that

specifies our url endpoint

here we pass an empty string that is a

string with no characters in it and this

represents the root of this app let me

show you what i mean so

imagine our app starts

at slash products

so if the user sends a request to this

endpoint they will be at the root of

this app potentially here we could have

other urls like slash products slash one

slash detail or slash products slash new

or trending or whatever so all the urls

in this app start with slash products

okay now back to the first example

what happens if we take away this slash

products we are left with nothing and

that is why we use an empty string here

now as the second argument to this

function we need to specify our view

function

so we defined that view function inside

of the views module

so first we need to import this module

into the urls module

now

this is how we do this from

period import views

period means the current folder so from

the current folder we are importing the

views module

so with this syntax we're telling django

to import the views module that we have

in this folder now you might ask wash

why didn't we import the views module

like this import views because views is

actually in the current folder so why do

we have to use the from import syntax

the reason for this is because views is

kind of a generic name so it is possible

that our project has a dependency to

another library called views

with this syntax python will end up

importing that module instead of the

views module in the current folder

because that will take priority

so

to remove these potential issues we use

the from import syntax

so now we imported the views module as

you know when we import a module that

module will end up being an object so we

can use the dot operator to access the

functions defined in that module so here

we want to reference the index function

okay let's delete it from here back to

our path function

as the second argument we type out

views.index

now note that i'm not calling this

function i'm simply passing a reference

to it django will take care of calling

this function at runtime when the client

sends an http request to the server so

here we should not call this function

so let's quickly recap what we have done

up to this point

in the views module

we created this view function and in

this view function we simply return some

plain text to the browser or the client

now i told you that nowhere django knows

that it should call this function so

that's why we added the urls module to

our app

and in this module we mapped the root

url to this view function

there's one more step left we need to

tell django about this app because up to

this point django is not aware of this

app

so

let's collapse the products folder and

open up the pie shop folder

in this folder we have another urls

module and this is like the root or the

parent urls module in our django project

let's open this

and scroll

down once again you see this url

patterns variable that is set to a list

in this list again we're calling the

path function

as the first argument we're telling

django that hey any urls that start with

admin delegate them to the admin app so

every django project by default comes

with this admin app which gives us a

beautiful administrative panel we're

going to work with that soon

so in this module we should also tell

django about our products app so let's

add another object to this list once

again we call the path function

now we tell django that hey any paths or

any urls that start with products slash

delegate them to the products app

so we want django to delegate the

handling of that request

to this urls module that we defined in

the products app

okay how do we do that very easy

back to the main or the parent urls

module on line 16 we have this import

statement let's expand it

so basically we have two import

statements look at the second one from

django.urls module we're importing the

pass function there is another function

that we need to import and that is the

include function

now we're going to use this function on

line 21 so as the second argument to the

path function we call include

and here we need to reference the urls

module in the product app so we type out

products dot urls

so take a look

in the products app

we have this module

urls that is why we type

products.urls but we don't type out dot

pi django will automatically take care

of that

now at this point you might be a little

bit confused or intimidated by all these

various steps that you have to follow

they may look foreign to you but trust

me this becomes second nature as you

practice building django applications

it's actually very easy it's just the

first time that you have to follow these

conventions defined in django framework

once you understand the concept it

becomes really easy

so basically because we created a new

app the products app only once ever we

need to write this line of code to tell

django that hey any urls that start with

products

send them to the urls module in the

products app

so we write this line of code only once

anytime in the future we want to define

a new view function first we go to the

views module we create a new function

and then we go to the urls module in

that app

and define a new url pattern to map that

view function to a url endpoint that is

really easy

all right now let's test our application

so back to the browser

let's head over to slash products

there you go you see our hello world

message here beautiful but if we

navigate back to the home page

we get this error page not found so our

beautiful django homepage disappeared

and the reason for this is that that

home page is automatically generated and

is only displayed when we first create a

django project

as soon as we define a new url pattern

and register it in our project that

homepage disappears but don't worry

we're going to come back and create a

new function for our home page later in

the course

now here is your exercise i want you to

modify this django project such that

when we navigate to products

slash new we'll see a page here with

some text like new products i strongly

encourage you to do this exercise

because it makes it really easy for you

to follow the future tutorials

alright here in the products app let's

open up the views module

in this module we define a new view

function so define let's call that

function new

as i told you before every view function

should take this request parameter

like here we want to return an http

response

with the text new products

that's it now to make pycharm happy we

add

another line break here so we have two

line breaks after the index function and

also two line breaks after the new

function these are the best practices

defined in pep 8 to format our code

so we're done with this view function

now we need to map it to a url endpoint

so we go back to the products app and

open up the urls module

here we need to add another url pattern

so we call the path function

the first argument should be new you

want to map this url endpoint to

views dot new function that's all you

have to do now back to our browser let

me navigate to products new we get this

message in the browser beautiful

in this tutorial i'm going to show you

how to create a model in a django

project a model is a representation of a

real world concept for example in an

online shop we could have models like

order customer shopping cart product

review and so on so let's go ahead and

create our first model

here in the products app

open up the models module

in this module we're going to create a

new class called product so let's delete

this comment we don't really need it

class

product

now we need to inherit this class from

the model class in django so in

parenthesis we type out models dot model

let's see what's going on here so on

line one from django.db package we are

importing

the models module

in this module we have a class called

model and this class defines all the

common characteristics and behavior for

models in a django application for

example we want to be able to store

these models in a database or read them

from a database or delete them these are

all the common operations that we need

to perform on these model objects

so by inheriting this product class from

this model class our product class will

have all these capabilities built into

it we don't have to code it okay so

colon now in this class we need to

define a few attributes what are the

attributes of a product that we need to

know in an online shop we need to know

their name

price

stock image and so on so let's define a

new attribute

we call it name and we set it to an

instance

of models the char field class

so once again in this module we have a

class called char field which is short

for character field and this represents

a field that can contain textual data

now here as a best practice we can

supply a maximum length to prevent a

malicious user or hacker from

accidentally storing a product with an

enormously large name this can mess up

with our application

so let's pass a keyword argument max

length and we set it to 255 characters

now let's define the price attribute so

we set price to models dot

float field so this represents a field

that can contain floating point numbers

that's it

now let's define the stock

we set this to an instance of

integer field

and finally let's define

image underline url

to an instance of models dot

one second char field

so in this course we're gonna use google

to find an image for our products for

example we can find this image

right click it

and copy its link address which is the

url

now if you open up a new tab and paste

that url you can see this is a very long

string

so we don't want to enforce a maximum

length of 255 characters

instead we want to use

2083

characters that is the standard maximum

length for urls so our product class or

product model has these four attributes

now to make pycharm happy and remove

this warning let's put the cursor at the

end of this line press enter then

backspace to remove the indentation

beautiful we should also add

two line breaks before this class so

here's one press enter the second line

break beautiful so our code is formatted

according to pep8 standards next i'll

show you how to use this model to create

a database table for storing products

in this django project we have created

you can see we have this file

db.sqlite3 this is an empty database

file that django creates and we use this

to store our data now sqlite is a kind

of database and it's the same place for

small applications but it's not suitable

for large enterprise web applications so

if you want to build a real enterprise

web application with django you need to

use a proper database engine like sql

server mysql oracle postgres and so on

the good news is that django supports

all of these database engines but sqlite

is the easiest to get started so we're

going to work with this for now and in

the future i will show you how to use a

proper database engine

now for the purpose of this tutorial i

want you to open up your browser and

search for db browser for sqlite

so on this page sqlitebrowser.org

you can find a very simple and free

application for opening sqlite databases

and as you can see here on the right

side there are executables for windows

mac and so on

so when you open it you get something

like this we can create a new database

here on the top or open an existing one

now here i'm going to drag and drop our

database file right here

you can see we don't have any tables in

this database so to store data first we

need to create a table for example to

store the list of products we need to

create a table called product and the

fields or columns we have in this table

should be exactly the same as the

attributes we have

in our product class

so in this tutorial i'm going to show

you how to use django to automatically

create this table we don't have to do

this by hand we can just tell django hey

here's our model go ahead and

automatically create a database table

for storing our products

that is very easy

so here down the bottom let's open up a

new terminal window and run python on

windows or python 3 on mac

manage.pi

make migrations

make sure to spell this properly so make

migrations in one word

now when you run this you get this

message no changes detected because by

default django doesn't know about our

product model

to solve this problem

we need to go back to our project

and open the pie shop package

in this package we have this settings

module for storing various configuration

settings for our project

so let's open this

and scroll down

on line 33 you can see a variable called

installed apps set to a list of strings

these are applications or apps that are

automatically installed with every

django project for example we have this

admin app which gives us a beautiful

administrative panel we're going to work

with it soon you also have this auth app

and we use this to authenticate users we

can put them in different roles give

them different permissions it's all

about authentication and authorization

we'll look at the other installed apps

in a future tutorial so for now let's

register our products app in this list

how do we do that

first we go to our project

inside the products app earlier i told

you about the apps module take a look

here

the name of this module is a little bit

misleading because we're in the boundary

of one app and we have a module called

apps

that aside all we have here is a class

called products config where we store

configuration settings for this

particular app

okay

now we need to go back to our settings

module and add the complete path to this

class including its package and module

so this class is defined in the apps

module and this module is inside of the

products package

so back to the settings file

in the list of installed apps we need to

type out a string like this

products that's our package

dot

apps that's our module

and then products

config

again make sure to spell this properly

so

p and c are capitalized because here we

have a class but products and apps are

all in lower case okay

so now django knows about our product

app so when we go back to the terminal

and run the last command we'll get a

different result

so use the up arrow to bring up the last

command and enter

there you go

now we get this message migrations for

products so inside the products folder

inside the migrations folder we have a

new module with this sequence number

called initial

let's have a quick look at the code

inside this module so back to our

products app let's expand the migrations

folder

here's our initial migration let's have

a quick look here

so we have a class called migration and

in this class

we have this attribute called operations

which is set to a list of operations so

every migration can contain multiple

operations look at the first operation

we have here migrations that create

model

so with this operation we can create a

new database table called product and in

that table we're going to have these

fields id name price stock and image url

these are the attributes that we created

in our product class but we didn't have

this id attribute django automatically

generates this because every database

table must have an id field and we use

this to uniquely identify records in our

database now let's go back to the

terminal

so we have a new migration but our

database is still in its previous state

we don't have a new table here yet

so we need to run this new migration to

generate our product table and that is

very easy

so one more time python

manage the pi

migrate

when we run this command django will

look at our project it will look at

every app and it will run the pending

migrations for that app against our

database so take a look when we run this

we get several messages

so if you scroll up you can see applying

content

types.001 initial so in the content

types app which is one of the apps

installed by default we have this

migration so django ran this migration

and this created a database table for

this app similarly in the auth app which

is used for authenticating users we have

this initial migration we also have a

bunch of migrations for the admin app so

django run all of these migrations and

down the bottom you can see

applying products initial migration

so every app can contain multiple

migrations and each migration will make

a slight change to the database to add a

new table or modify an existing one

so back to db browser for sqlite let's

drag and drop our database file one more

time here to reload it there you go now

we have 12 tables in this database each

table is prefixed with the app it

belongs to for example you can see we

have a table for storing our users we

have another table for storing the

groups a user belongs to we have another

table for storing permissions and so on

now here down the bottom you can see

is table products underlined product so

this product table is prefixed with the

name of our app which is products

now if you expand this you can see

these fields in this table id name price

stock and image url so this is the

beauty of django we didn't have to come

here and manually create these tables by

hand that's very time consuming we

simply created a model with these

attributes and then we ran two commands

in the terminal one for creating a new

migration based on the changes we have

made in our code and the other to run

the pending migrations so now all the

migrations in this project are run

against our database which means if we

go back to the terminal and run python

manage.pi migrate

we get this new message no migrations to

apply

so here's the workflow next time we

create a new model or modify an existing

one we should come back here in the

terminal create a new migration and then

run it

alright here's your exercise we want to

have the concept of offering discounts

in our imaginary online shop

so i want you to create a new model

class called offer

and in this class we should have three

attributes

one is code which is a textual field for

example our offers code could be vca2142

it's just a coupon code

here we should also have an attribute

called description

again this is going to be a textual

field for example we can say 20 percent

of all products and then we can display

this text somewhere on the home page in

the future

and finally we need another attribute

called discount which is going to be a

floating point number like 0.2 for 20

discount so go ahead create this model

class next create a migration and run it

to bring our database up to date this is

an awesome exercise for you to get your

hands dirty in django so spend three to

five minutes on this exercise when

you're done come back see my solution

so here in the models module right after

our product class i'm going to define a

new class

class offer

this class should also derive from the

model class in django

here we add the attributes so

the first one is code which is going to

be an instance of models dot char field

and we set the max length to let's say

10 characters

next we add the description

once again we're going to have a chart

field with max length of 255 characters

is sufficient and finally we need

discount

and we're going to set this to an

instance of models that float filled

so here's our offer class now we need to

create a migration so over here i'm

going to open up a terminal window

this is the main terminal window where

our web server is running so i'm going

to create a new terminal window and run

python

manage dot pi

make

migrations django detected a change in

our models so it created this new

migration migration number two called

offer and this migration will create the

offer table in our database so let's go

ahead and run it

python3

manage.pi migrate

beautiful

now let's drag and drop our database

here one more time

our database is refreshed as you can see

in the products app we have this new

table offer with these four columns

id code description and discount

in this tutorial i'm going to talk to

you guys about the administrative panel

of django applications so here in the

browser if we head over to slash admin

we get this beautiful login screen to

log into our administrative panel so

every django application by default

comes with an administrative panel we

don't have to create this from scratch

we don't have to code this it gets

auto-generated and this is one of the

fantastic features of django that

increases your productivity so let me

show you how to work with this

administrative panel

here in pycharm we need to create the

first user of this application we call

that super user

so here in the terminal window let's run

python

manage dot pi

create

super

user all in one word

so let's go ahead with that it asks for

username let's type admin

next we need to enter an email address

i'm going to enter my email address next

we need to enter a password i'm going to

type one two three four

and repeat it one more time

note that it complains because this

password is too short it's too common

and it's entirely numeric

so at the end it asks if you want to

bypass password validation for

simplicity let's go with that but of

course in a real scenario you'll want to

create an admin user with such a simple

password

all right we successfully created the

super user

now back in the browser let's log in

with admin and one two three four

there you go

so this is our administrative panel as

you can see we can manage the users and

groups we can add new users or modify or

delete existing ones let's have a quick

look here so here we have this search

bar on the top we can quickly search for

users below that we have this table of

users with this columns username email

first name last name and status we can

sort this table by any of these columns

we also have these filters on the right

side

so we get all these beautiful features

for free with every django application

we don't have to code this

earlier in this course we talked about

this settings module let's have a quick

look here

in this module we have

a setting or variable called installed

apps and one of the apps that is

installed by default is the admin app

so this app is the piece that is

responsible for generating these views

now the beautiful thing about the admin

app is that it is easily extensible so

back to the home page of our

administrative panel so far we can only

manage the users and groups but using

one line of code we can also manage our

products let me show you

let's expand our products app

inside of this app we have this module

admin and in this module we register the

models that we need to manage in the

admin section

so let's open this module

now on the top

first we need to import our product

model so we can type out some code like

this from period models that means the

models module in the current folder

so from this module we want to import

the product class or the product model

right

now you can see this comment here

register your models here let's delete

this comment we don't need it anymore

instead we're going to write code like

this so admin

dot site dot register

and we pass this product class as an

argument what is going on here

we're using this admin object that is

imported

on line one this object has an attribute

called site which is an object itself

this object has a method called register

we're calling this method and passing

our product class as an argument with

this we're telling django that we want

to manage our products in the admin area

so now with only one line of code or

more accurately two lines if we go back

to our administrative panel and refresh

this page

we see this new table products that

represents our products app and in this

app currently we only have one model

called product so here we can manage all

our products currently we don't have any

products in our database so let's go

ahead and add a new product look we get

this beautiful form for free we didn't

write any code to create this form and

handle the click event of these buttons

to insert a product into our database

all this is automatically generated by

django

so let's go ahead and add a new product

call that orange let's say 1.99 each

and

set the stock to 50.

now we need an image url so open up a

new tab here

and in google search for orange

then

go to images

click on tools

from the user rate menu select for

labeled for reuse this way we don't have

problem with copyright issues so these

are the three images that we can use in

our application

let's pick this one

click on it again

now on this page right click the image

copy a link address

and then back to our product form

paste it here

and then save

so we successfully added a product and

that product is listed here in the

product table but what we see here is a

little bit confusing it says product

object one it's not clear what product

this is is it an orange is it a

strawberry what price is it so in the

next tutorial i will show you how to

customize this table and add columns

specific to products

in this tutorial i'm going to show you

guys how to customize this products

table in the admin area that is very

easy so back to pycharm

here in the admin module where we

register the product class for

administration we need to create a new

class called product admin so

we create a class

called product admin so this is the

convention we follow in django we start

with the name of our model that is

product and then we add the suffix admin

now we should inherit this class from

admin

dot model admin what is going on here

well this admin is a module that we have

imported on line one

in this module we have a class called

model admin which provides all the

common functionality for managing models

in the admin area so with deriving this

class from the model admin this class

inherits all this common functionality

now

in the body of this class we can

overwrite or change some of this

functionality or attributes for example

in this class we have an attribute

called list

underline display and this attribute

specifies the columns that should be

visible in this table

so we set this to a tuple

and in this tuple we add one or more

attributes of our product class

so let's quickly open up our product

class

it's here in the models module

okay there you go so our product class

has these attributes name price stock

and image url now image url as you saw

is a long string so we don't want to

display that in our table so in this

tutorial let's add these three

attributes to our products table

back to the admin module

in this tuple we add three strings name

price

and stock

now we have this little warning here

because we haven't added two line breaks

before and

after this class

that is better

finally when registering our product

class for administration

as the second argument we need to pass

this new class product admin

so django will use the information in

this class to decide how to present the

list of products

so back in the browser let's refresh

this page there you go here's our

products table now we have three columns

name price and stock you can see we have

this orange the price is set to 1.99 and

currently we have 50 items in the stock

beautiful let's go ahead and add a new

product here

let's say strawberry

and the price 2.99

30 for the stock and finally we need an

image url i'm going to paste this

address that i just copied before

recording this video okay let's go ahead

save the changes

the product is added beautiful and now

we have two products in our table now

here's what i want you to do i want you

to pause the video and add a few more

products to our database somewhere

around 5 to 10. in the next tutorial i'm

going to show you how to display these

products to the public users of our

website because this admin panel is only

visible to admins so anonymous users or

other registered users are not going to

have access to this panel instead

they're going to go to

slash

products

and currently we're displaying a hello

world message we're going to change this

page and display the list of our

products in a beautiful grid so pause

the video and add five to ten products

then come back continue watching

currently in the admin area we can only

manage the products in the products app

so there is no way to manage the offers

so as an exercise add the ability to

manage the offers here when we click the

offers link we should see a table with

two columns code and discount

so go ahead and implement this and then

create a new offer

all right here's my solution

in the admin module of the products app

on line two first we need to import

the offer class

next

we create a new class called offer admin

we derive this from admin that model

admin

and here we set the list display

attribute to a tuple with two items

code

and discount

and finally we need to register our

offer model for administration

so admin.site.register

offer and offer admin

that's it

now if we go back to the admin area

and refresh the home page we see the

offers link here beautiful currently we

don't have any offers so let's go ahead

and add a new offer

i'm going to use the code like vca 1010

let's say 10

off all products

and discount i'm going to set this to

0.1

now technically in a real application

this code should be unique but that's a

topic for a future tutorial so for now

don't worry about it let's go ahead and

save this offer

okay our offer is saved successfully

beautiful as you can see in this table

we have two columns code and discount

in this tutorial i'm going to show you

guys how to replace this hello world

message with the list of products in our

database and that is super easy

so here in pycharm in the products app

let's open up the views module

area i told you that in this module we

define our view functions which are

functions that get called when the

browser sends an http request to the

server

for example when the user navigates to

slash products page our browser sends an

http request to our django application

django takes that request and hands it

off to this function the index function

and here we're simply returning a hello

world message we want to replace this

with the list of products in our

database

so the first step is to get the products

stored in the database and then we need

to format them using some html template

so let's go ahead and

on the top import our product class from

the models module so

from

period models

import product so we're importing the

product class in the models module in

the current folder so period means the

current folder

now this product class has a bunch of

useful methods for getting data from our

database for example we can call

product.objects.all

and this returns all the products we

have in our database we also have filter

for filtering products let's say we want

to get products that are more expensive

than two dollars or products that are

out of stock we can use the filter

method we also have the get method for

getting a single product and we also

have the save method for inserting a new

product or updating an existing one now

in this tutorial we're going to use the

all method to get all the products from

our database

then we store them here in this variable

so we have done the first step next we

need to create an html template for

presenting this list of products to the

user so back to the project panel

inside the products app

let's add a new folder a new directory

and by convention we should call that

templates make sure to spell it properly

because this is a special directory that

django looks at the load templates

so let's go ahead with that now we want

to create a template for the index

function so inside of this folder let's

add a new file

and call that file index

dot html

now here we can write some html code if

you're not familiar with html don't

worry just follow along with me it's

super easy to learn

so first let's type h1 and then press

tab

this inserts an h1 tag into our html

document and we use this to display a

big bold heading so inside these tags

let's type products

now below this h1 let's type ul and

press tab

now this inserts a ul tag and we use

this to display a list of items now we

need to surround each item with an li

tag so type out li press tab

and in between the tags let's type item

1 then copy and paste this a couple

times so item 2 and item 3. now instead

of item 1 item 2 and item 3 we want to

display the name of our products but

before we get there let's simply return

this html markup to the client instead

of the hello world message

so back to the views module

here in the index function we need to

change the return statement on line 8.

so

you want to call the render function

this function is already imported on the

top on line 2. we use this function to

render a template

so

let's call this function as the first

argument we need to pass

this request object that we get as an

argument to this function

so let's pass the request here

as the second argument we need to

specify the name of our template so we

pass a string what is the name of our

template that is

index.html right now before going any

further let's go back to the browser

and

refresh this page

so instead of hello world we see this

product's heading this is the result of

an h1 tag and with ul and li tags we see

these bullet points over here beautiful

now finally we need to replace item one

item two and item three with the list of

our products

so back to our view function

as the third argument to the render

function we need to pass the list of

products that we loaded from the

database so here we need to pass a

dictionary

in this dictionary we're going to add

one key value pair we're going to call

the key products but we could call it

anything it doesn't really matter

the value for that key should be the

products object that we define on line

7.

so

here in our dictionary let's add this

key product

colon and the value should be

this product object

so let me break up what we have on line

eight

over multiple lines so you can see it

clearly

recording the render function with three

arguments the request object the name of

our template and a dictionary that

contains the data to be passed to this

template

and finally we're going to go to this

template

index.html

and replace these items with our

products that is very easy

so just after the ul tag i want you to

type out a curly brace followed by a

percent a space a percent one more time

and a closing brace

this is what we call a template tag in

django so in between these markers we

can write dynamic code for example we

can add loops to repeat some

instructions or write if statements to

conditionally render some content

so here we want to write a for loop for

product

in

products

so earlier in our view function we

passed these products here using a

dictionary back to the view function

look

as the third argument to the render

function we passed is dictionary this

dictionary is called the context so it

provides data to be used in our

templates in this case we have a

property called products and that is the

reason we can access it here so we are

looping over this product

now for each product you want to render

a list item so let's indent this item

here

and

replace item 1 with the name of the

product so here we want to dynamically

render the name attribute of this

product object

to do that we use double curly braces so

open two curly braces and close them and

in between them type out product dot

name so whenever we use double curly

braces in a django template django will

evaluate the expression that we put here

and render it in html

now the last step is to end this four

block because django unlike python

doesn't rely on indentation to determine

the scope of a block

so

right after this for loop once again we

add curly braces eight percent and type

out and four

and then we close it here

now we no longer need these items here

so let's delete them

now back to the browser let's refresh

our page

so instead of item 1 to 3 we see the

name of the products stored in our

database

now let's take this to the next level by

displaying the price of each product

right next to it

so

back to our template this is where we're

rendering the name of the product

after the curly braces let's add

parenthesis now inside of the

parenthesis we want to dynamically

render the price of each product so once

again we use

the double curly brace syntax to render

some value dynamically that is the value

of product dot price

like this

now back here let's refresh the page

now we can see the price of each product

right here beautiful we could also

prefix that with a dollar sign so before

the curly braces we add a dollar sign

and then when we refresh the page we see

the actual dollar value

so this is what i want you to take away

in this tutorial in django templates we

have two special syntaxes one is a curly

brace and a percent this is called a

template tag and we use this to

dynamically execute logic

so in between these template tags we can

write for loops to repeat some code or

we can use if statements to dynamically

render content

the other syntax we have is the double

curly brace syntax and we use this to

dynamically render values in our html

markup so whatever we put in between

them will get evaluated and written to

the html markup

now this page is pretty boring so far in

the next tutorial i will show you how to

convert these bullet points into

beautiful cards

over the next few tutorials we're going

to replace this boring list of bullet

points with a beautiful modern card like

this so on the top we're going to

display the image for each product below

that we're going to display the title or

the name of the product as well as the

price and potentially a button to add

that product to a shopping cart now to

present something like this we're going

to use a framework called bootstrap it's

a very popular framework for building

modern and responsive applications so

head over to getbootstrap.com

on the home page

you should see something like this and

then go to the documentation

on this page you can see how you can add

this bootstrap framework to your web

applications so if you scroll down

here you should see a starter template

so here we have some basic html markup

we want to bring all this html markup

and store it in a template called

base.html so over here you should see

this copy button click that to copy this

then back to pycharm

in the project panel

inside of the templates folder let's add

a new html file so a new file we call

this base.html

now

with command and v on mac or ctrl and v

on windows paste all this markup that we

copied from bootstrap website

now

here on line 13

we have the body tag and this is the

container for what the user sees in a

given web page

now in this example we have an h1 tag

for displaying a hello world title we

want to replace this with something

dynamic so for each page in our

application we want to render something

different for example when the user goes

to the products page over here instead

of this h1 tag we want to render what we

defined in index.html here

okay

so back to base.html let's delete this

h1 tag once again we're going to use a

template tag so curly brace percent

percent curly brace

now the template tag we're going to use

is called block and with this we can

define a block or a hole in this

document so we're going to create a

block called content we could call it

anything but here we're defining the

content area of our website

so that's why we call this block content

now after this once again we need to add

another template tag

and this is called end

block now we should go to index.html

on the top we should tell django that we

want to extend this base template which

means we're going to use all the markup

defined here

and this gives our applications a modern

look and feel

so back to index.html once again we're

going to use another template tag

this one is called extends so extend

what are we extending

the template defined in base.html so

here we add a string base

dot html

now we want to fill the block or the

hole that we defined in base.html

with

these view lines

so once again we add a template tag

block what is the block that we're

filling that is the content block right

and we close it here

so now all this markup is going to go

in the content block

now finally we need to close this block

so after the last line

let's add another template tag

and block

now to make this code cleaner i would

prefer to select these few lines that

belong to the content block and

indent them like this this is not

required but it just makes our code

easier to read

so with these changes that we made in

this tutorial when django tries to

render this page

first it will look at base.html so it

will take all the markup defined in that

file and then it's going to fill

this content block with the markup we

have defined here

now if we go back to our browser

and

refresh this page we're going to see

something a little bit better so refresh

you can see the fonts are changed and

there is a little bit more space in

between the bullet points

now you're ready to replace each bullet

point with a bootstrap card and that's

what i'm going to show you next

in this tutorial i'm going to show you

how to display these beautiful cards on

our products page now note that this

page is responsive so if you view it on

a small mobile device we're going to

have one card on each row

like this

and if you view this on a bigger screen

we're going to have more columns or more

cards on each row so let me show you how

to build this

first head over to get bootstrap.com

click on the documentation

here on the left side you can see a link

called components

on this page you can see all the

components that are defined in bootstrap

these are the components that we can add

to our web pages to make them beautiful

and modern

so the component that we're going to use

is called a card

over here you can see

an example of a card

and right below that you can see the

markup that we need to use to render

something like this

so

let me resize this screen okay on the

top right corner we have this button

copy this markup

now back to index.html

instead of rendering a ul and a bunch of

lis we want to render a bunch of divs

because with ul and li we'll get bullet

points but we don't want to display

bullet points here

so

right below the h1 tag

type out div dot row and then press tab

so this creates a div with the class row

now in this row we want to repeat

multiple columns so type out div

dot

call as in short for column and then

press tab

so we use this divs to create a layout

like this we have multiple columns in a

row

okay

now inside of a column

we want to render a card so now we

should paste the markup for rendering a

bootstrap card

so paste that here

now we can see our code looks a little

bit ugly because it's not indented

properly so on the top go to the code

menu

here we have this item reformat code and

look at the shortcut that is associated

with this command so let's click that

now our code is beautifully formatted

and it's easier to read and modify

so we have a row inside this row we have

a column and inside this column we have

a card

now we're going to take our for loop and

put it above this column

so for each product we want to render a

column

so scroll down

and

grab this line of code cut it

and then

paste it right above

this column

now we should close this for loop so

let's collapse this div below it

okay now right after this div we want to

add a template tag

and type out and four

with these changes we don't need the

code from before we don't need the ul

and li tags so let's delete all of these

so this is the final result

inside the content block we should have

these tags

we have an h1 on the top for the heading

below that we have a row

then we have our for loop and in each

iteration we render a column so let's

also indent this line to go inside the

for loop that's better and finally we

close our for loop and after that we

close our row

with this change if we go back to the

browser

and refresh

we get something like this we're

basically repeating all that static or

fixed markup from bootstrap over here

so we're not rendering the actual name

or the image of each product but that is

a very easy fix

so back to our markup let's expand this

column

so here's our card

inside this card we have an image on

line nine look at the source attribute

of this image

we need to change this

and dynamically render the image url

attribute of each product so let's

delete this

and inside the quotes we add double

curly braces to render some value we

want to render product dot image

underline url

like this

now over here on line 11 we have this

text card title we want to replace this

with the name of each product so delete

double credit braces and we add product

dot name

next we need to replace this text

with the price of each product so delete

here we have a paragraph tag inside this

tag we add double curly braces to render

product dot price and just before these

braces we want to add a dollar sign

and the last change

is the label for this button

it's called go somewhere we want to

change that to add to cart

now back to this page refresh we should

get something like this beautiful

in this tutorial i'm going to show you a

couple of techniques for improving the

look and feel of this page first we're

going to add a navigation bar on the top

and then we're gonna add some padding

around with elements currently this

product card is way too close to the

left side of the screen so we should add

some padding to let this page breathe

now to add a navigation bar

once again we go to the bootstrap

website look at the documentation for

the navbar component so here's the

navbar

now if you scroll down

you can see a typical nav bar so we can

have these links we could have a drop

down we could have a search bar now this

looks a little bit clunky because i've

resized the screen so it doesn't look

pretty but below that you can see

another

simple navigation bar with only the

brand or the name of the application

so over here we have the markup to

render this navigation bar so let's go

ahead and copy this

now back to pycharm where should we add

this markup

we should add it to base.html because

this is supposed to be a base template

for all pages in our application

so

here's the opening body tag right below

this body tag we want to paste the

markup for rendering a navigation bar

now the code is not formatted properly

it looks clunky so once again go to the

code menu and then reformat code as you

can see the shortcut for mac is alt

command and l so i'm going to use a

shortcut here

there you go that is better

so here's our navigation bar

now let's change this text from navbar

to

pi shop that's the name of our

application right

now back to the browser

let's refresh this page we have this

navigation bar on the top let's go back

to pycharm and make a slight change in

the structure of our application

so here in the products app we created

the templates folder and in this folder

currently we have two templates the base

template for our application and the

template for the products page the

problem with this structure is that this

base html is not reusable because we

have added it inside the template of the

products app what if in the future we

want to add another app to this project

we don't want to recreate this base.html

in every app that just doesn't make

sense so we want to reuse this across

multiple apps and that's why we need to

move this outside of this folder and put

it somewhere central so

in the root of our project

here we need to add a new folder called

templates so right click the project and

add

a new directory

called templates

now we want to go back to the products

app

inside the templates folder

we drag this base.html file and drop it

into the main templates folder

okay

good now our base template is somewhere

central so we can reuse it in multiple

apps

however if we go back to the browser and

refresh this page we get this error

template does not exist

if you scroll down you can see why we

get this error

so over here you can see this red line

let me zoom in

this error happens because django

couldn't load

base.html

now if you scroll up

you can see the paths that django

searches for to find this template

here's the first path

admin slash templates slash base.html so

django is looking for this template

inside the admin app

here's the second path aus slash

templates slash base.html so django

couldn't find it in the admin app it

thinks maybe it's in the us app and

finally here's the last pass products

slash templates slash base.html that is

our products app so what is going on

here django is looking for this template

only inside of the installed apps

but this templates folder that we

created it's not really part of any apps

it's just a standalone folder

so we need to tell django to look inside

this folder in addition to the installed

apps and that is very easy

so

in the main package pi shop

you have seen the settings file before

let's have another look here if you

scroll up

you can see this variable base directory

this variable is set to the complete

path of where you have stored this

django project on your disk

we're going to take this directory and

append templates to it

so

scroll down

on line 55 you can see the configuration

for loading templates

look at the settings we have here the

first setting is back end and this is

the engine that is used to parse our

templates so all those template tags as

well as the double curly braces this is

the engine

that knows how to interpret those

look at the second setting

directories this is set to an empty list

so here we need to reference the

templates folder in this project

so let's type out os

dot path so we're using the path object

defined in the os or operating system

module that is important on the top now

this path object has a method called

join and with this we can join multiple

parts of a path

the first part

is base underlined

which is the variable that i showed you

earlier it's set to the complete path of

your django project

now we want to take this and append

templates to it

that's all you have to do so back to the

browser let's refresh the page there you

go the problem is fixed so now our base

template is somewhere central and we can

reuse it across multiple apps beautiful

and one last change

currently as you see these items are so

close to the left side of the screen so

i'm going to add some padding to make

this page breathe and that is very easy

back to pycharm

here in our base template

where we define

this content block we need to wrap this

with a div with the class container this

is one of the classes defined in

bootstrap that we use to define a

container area in our application this

container area has some padding so type

out div dot container and press tab okay

and then move these template tags inside

of this div

that's it now back to the browser let's

refresh

so this is our container area as you can

see we have some padding to the left and

right side of this container area

beautiful

so that brings us to the end of this

django tutorial in this python course i

hope you learned a lot and thank you for

watching

so that was a short and sweet

introduction to django but django really

requires his own course and i'm planning

to create a comprehensive course on the

topic in the near future now here's a

question for you

what kind of applications do you want to

build with django use the comment box

below and let me know i will take your

ideas into consideration as part of

creating my upcoming django course

so that brings us to the end of this

course i hope you learned a lot please

support my hard work by liking this

video and sharing it with others and

also subscribe to my channel for more

tutorials like this thank you so much

for watching and i hope to see you again

soon

[Music]

you