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Hi and welcome back. 2

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In this video, we're looking 3

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at default values for parameters. 4

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If you already know a bit of Python, 5

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you may wonder why we didn't cover this earlier. 6

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And quite simply the reason is that we didn't need it. 7

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Now we do and we're gonna start looking 8

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at a couple of instances where having default values 9

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with parameters is gonna be useful. 10

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So let's get right on it. 11

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Whenever we call a function that has parameters, 12

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we are expected to give it an equal number of parameters. 13

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We already know this, so I'll show you some example code. 14

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Here's some accounts, like a checking account. 15

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Let's see, that has $1,958 in it 16

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or pounds if you're in the UK. 17

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3695.50 in your savings. 18

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That's a pretty respectable amount of money. 19

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Then we're gonna have a function add_balance, 20

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which is going to take an amount, 21

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which is going to be a float and a name, 22

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which is going to be a string. 23

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And it's going to return a float. 24

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The reason I'm including it here, 25

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the type hinting that we've looked at in the past. 26

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Also, just for completeness, I am going to say function 27

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to update the balance of an account 28

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and return the new balance. 29

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Include that log string in there 30

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just so you know what this function's all about. 31

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As you can see, this function, add_balance, 32

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is going to update the balance of an account 33

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and return the new balance. 34

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The two arguments it takes are the amount 35

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to increase the balance by 36

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and the name of the account that we're gonna change. 37

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Then it's gonna go over to your accounts global dictionary 38

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and it's going to change it. 39

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So, accounts name 40

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plus equal amount 41

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and then it's going to return accounts name. 42

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It's going to return the new balance of the account. 43

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Accounts name, for example, for checking 44

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is going to be 1958. 45

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Let's say we say 200 in here is gonna go, 46

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increase it by 200. 47

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I'm not even gonna try to do the math here. 48

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Then it's going to return the new amount 49

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of accounts name, so that should be a float. 50

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However, what we can do, of course, 51

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is add balance 500.00 to savings 52

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and then print account savings 53

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and it should tell us the new balance 54

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which should be in the four thousands. 55

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Oh, sorry, accounts savings. 56

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As you can see, 4,195.5. 57

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Notice how the zero at the end gets dropped, 58

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but in my code I like having two decimal places 59

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for currency just to keep things clearer. 60

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What you didn't know that you could do is you can say 61

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that by default, all new balances are going to go 62

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to your checking account. 63

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So the name here is going to be checking, by default. 64

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And the way we do that is we add equal checking. 65

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Okay, so the name is a string 66

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and its' default value is checking. 67

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That means that if we do not pass a string 68

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through this argument, which we can do now, 69

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we can not pass a string to it. 70

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We can not pass anything to it 71

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and we print out the checking at the end, 72

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we should see it has increased by $500, 73

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not 500 units. 74

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If you don't wanna use type hinting, 75

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then all you have to do is get rid of that. 76

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Okay and this stays the same, name equals checking. 77

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And that's that, okay. 78

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Frequently, actually, if you don't have type hinting, 79

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you'll see this written like so, without the spaces 80

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and when you do have type hinting, 81

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you'll see it written like so, all with spaces. 82

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It's up to you how many spaces you want 83

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to put in there, whether you wanna put spaces 84

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or not spaces, totally fine. 85

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Now, something important that you have to know 86

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about these names arguments, this is what they're called 87

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as soon as you have the default argument there, 88

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is that you cannot have this 89

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here, oops sorry, 90

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you cannot have this here. 91

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This will be illegal. 92

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When you run it, it'll tell you here. 93

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Syntax error, known default argument 94

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follows default argument. 95

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So you cannot do this. 96

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Any argument that has a default value 97

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has to follow arguments that do not 98

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have default values. 99

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So in this case, the amount 100

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does not have a default value. 101

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The name does, so the name has to go at the end. 102

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If you have many arguments, 103

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some of which have default values, 104

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they must all go at the end. 105

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Okay? 106

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That's it. 107

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This is default values for arguments. 108

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You can have many arguments, many default values. 109

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One default value per argument, 110

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of course and we're gonna learn more 111

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about these default values 112

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and how to use them in subsequent videos, 113

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in just a couple of videos. 114

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In fact, in the next video, 115

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and in coming videos too. 116

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So, that's it for this one. 117

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I'll see you on the next one.