All language subtitles for 04_getting-started.en

In this course,
you're going to learn to write computer

programs in the Python
programming language.

But before we get into that, we need
to know exactly what programming is.

Fundamentally, programming is
giving a list of instructions for

a computer to follow.

In the contest of programming,

this instructions are sometimes
called algorithms.

Now computers are really good in following
this instructions very reliably and

very quickly but not very creatively.

And we can't just give computers
instructions in English or any other

natural language that we normally speak
because natural language has ambiguity.

Words or sentences can have multiple
meanings which computers can't figure out.

Instead we need to give computers
instructions in a programming language,

which is a kind of language
that computers can understand

because they have a formal syntax or
set of rules.

There are many programming languages that
exist including JavaScript, C++ Java,

Haskell and many many more.

But in this course we're going to learn
to use the Python programming language.

The process of learning programming is
more than just learning the rules of

the Python programming language.

It's also about how to breakdown and

solve problems regardless of
the programming language.

And I like to think of programming as a
translation process, where the programmer

translates their goals from natural
language into a programming language.

For example,

if I want to write my own version of
the game Wheel of Fortune, then I need to

translate the rules of the game into an
unambiguous set of instructions written in

the Python programming language that
tell the computer how to run the game.

And as you become a programmer, you'll
learn how to come up with strategies, or

algorithms, for solving problems in
how to translate these strategies

in the Python code that
a computer can execute.

Now, all that said, the best way to learn
programming is through practice, so

let's get started.

In this course, you'll be able to write
Python codes right in your browser.

You'll see what are called
active code windows

that look like this in your textbook.

Now, most programming courses start off
with what's called a Hello World program

or a program that prints out Hello World
on the screen when you run it.

In Python, a program to print
Hello World looks like this.

In order to actually run this code,
we need to click the Save & Run button.

When we do that, we'll see an output
window show up to the right here.

Now to break down what all of this shows,

we have our Python
source code on the left.

And we have our output on the right.

Now, when we click Save & Run what
happens is that there's a hidden Python

interpreter.

And it looks at what's in our source code,
and

prints out whatever any
relevant output is.

And remember that this source
code is a set of instructions.

In this case, the source code
is an instruction to print out

whatever is in quotation marks here,
in this case, Hello World.

If we wanted to change the set
of instructions, so for

example, I want to change it to print out,
Hello Michigan.

Then I need to put it through the
interpreter by clicking Save & Run again,

and now when I do that,

you'll see that my output changed
from Hello World, to Hello Michigan.

If I want to change it back,
Then I need to click Save & Run.

Now, the Python interpreter typically
tries to run all of the source

code that we put in this window.

But it can sometimes be helpful to leave
natural language notes or explanations for

ourselves or for other programmers
who are looking at the source code.

Now the Python interpreter
typically tries to run

all of the source code that we put
into our source code window, but

sometimes it can be helpful to leave
natural language notes or explanations for

ourselves or for other programmers
looking at the source code.

In order to do that,
we have what are called comments.

In Python, we write a comment
by using the # symbol and

writing what we want after it.

When we write a comment, then Python
ignores everything that comes after the #

symbol, meaning that we can
write whatever we want here.

And on the next line,
Python will start running the code again.

So if we wanted to write a comment,
we would need to add a # symbol.

And what comments do are they tell
the Python interpreter to ignore

these portions of the source code,
and only to run what's not commented.

In our case, the only code that actually
runs here is print Hello World.

Another thing that's worth noting is
that the Python interpreter is not very

forgiving.

So recall that when you write source code,
you're giving the computer a set of

instructions, and
these instructions need to be unambiguous,

they need to follow the rules of
the Python programming language.

One of the rules of Python is that
when we have an open parenthesis,

then we are going to need to
have a closed parenthesis.

So, let's suppose that
I forget that rule and

I delete this closed parenthesis,
and I try to run my program.

What happens is that I get
what's called a syntax error.

A syntax error is Python saying that it
doesn't understand the rules of what you

wrote, so it doesn't try to actually
execute what's in the source code window.

In other words, a syntactic error or
a syntax error is when

you are not following the rules of
the of the Python programming language.

In this case, we are not following
the rule that this open parenthesis

has to be followed by
a closed parenthesis.

Throughout this course,
we're going to run into syntax errors and

other kinds of errors, including run
time errors and semantic errors.

So when we get a syntax error, as we
will many times throughout this course,

we can fix it by editing the source
code to obey the syntactic rules of

the Python programming language.

In this case,
I'm going to add a close parenthesis

to match the opening parenthesis
that starts out here.

Now when I click Save & Run again,

then you'll see that the syntax error
disappears and my program runs again.

With that, you're already on your
way to becoming a programmer.

With more practice, you'll better
understand how the Python interpreter

works, and will be able to write larger,
and more complex programs.

See you next time.