Functions - The basics |Section 3|Celestial Warrior

1

Show more

00:00:00,500 --> 00:00:06,120

Hi again, in this video you'll learn how

to create a function in Python and how

3

00:00:06,120 --> 00:00:13,380

to use that function, so let me go ahead

and create a script. Let me name this my

5

00:00:13,380 --> 00:00:23,730

function.py and let's go ahead and

create a function. Creating a function

7

00:00:23,730 --> 00:00:30,210

will always begin with the DEF keyword

which is, which means define. Now that is

9

00:00:30,210 --> 00:00:33,980

followed by the name of the function, so

you need to give your function a name

11

00:00:33,980 --> 00:00:43,350

let me name this minutes to hours and

as you may guess already what I'm

13

00:00:43,350 --> 00:00:50,910

creating is a function that will convert

minutes to hours, so you create the

15

00:00:50,910 --> 00:00:56,940

procedure on how to convert minutes to

hours and then you can call that

17

00:00:56,940 --> 00:01:02,129

procedure, so you can call that function.

You can give that function any values

19

00:01:02,129 --> 00:01:07,380

when you call it and the function will

produce an output depending on the value

21

00:01:07,380 --> 00:01:12,659

and depending on the formula, on the

procedures that you write in here, so

23

00:01:12,659 --> 00:01:16,860

let's go ahead and do that, minutes

to hours. Now functions normally they have

25

00:01:16,860 --> 00:01:23,549

some input and they produce some output.

The input goes inside these brackets

27

00:01:23,549 --> 00:01:29,130

here. In our case the input could be

minutes so this is just a variable, you

29

00:01:29,130 --> 00:01:32,430

can give it any name that you want, you

can give it any name that you want for

31

00:01:32,430 --> 00:01:38,939

the function name as well, so the input

is minutes and then the output will be

33

00:01:38,939 --> 00:01:43,610

hours, but you don't write the output here.

Here what to do you always choose a

35

00:01:43,610 --> 00:01:52,340

column, press enter and that will be auto

indented, so as you see the functions

37

00:01:52,340 --> 00:01:56,969

everything that you write below the

first line of a function definition is

39

00:01:56,969 --> 00:02:02,850

indented and every line after that, so the

DEF keyword, the name of function, the

41

00:02:02,850 --> 00:02:09,720

input and here we write the body of the

function. What we want to do is let's

43

00:02:09,720 --> 00:02:18,850

say variable house equals to

minutes / 60 that should give us the

45

00:02:18,850 --> 00:02:26,290

hours. Note that if you are on Python 2

you want to do 60 point zero because

47

00:02:26,290 --> 00:02:31,540

if you do that you get an integer as

an output, not a float, so in

49

00:02:31,540 --> 00:02:37,030

Python 2 you have to explicitly pass

a float when you do division to get a

51

00:02:37,030 --> 00:02:42,190

number, to get a float with decimal

point. I am in Python 3, so I don't

53

00:02:42,190 --> 00:02:48,340

need to put 60.0 there. And yeah, this is a

simple function, so this is what the

55

00:02:48,340 --> 00:02:52,450

function will perform and then the last

line of the function is normally a

57

00:02:52,450 --> 00:02:59,790

return keyword, so notice that these are

reserved keywords def and return, and

59

00:02:59,790 --> 00:03:06,430

what I want to return is, well gets what?

The output which is hours, so that's the

61

00:03:06,430 --> 00:03:11,769

idea, we are getting minutes. The user

will input a value for that later when

63

00:03:11,769 --> 00:03:17,230

you call a function and Then minutes

will be divided by 60 and that operation,

65

00:03:17,230 --> 00:03:22,810

that number will be stored in the hours

variable which is a variable that exists

67

00:03:22,810 --> 00:03:27,700

only inside the function so this is

called a local variable. If you call it

69

00:03:27,700 --> 00:03:32,470

outside the function it will not work,

but we'll cover that later. And so then

71

00:03:32,470 --> 00:03:41,130

we return the value of that variable.

Now I'll save this and open the terminal.

73

00:03:45,359 --> 00:03:58,329

Make some space there and let me execute

the script. You get nothing and the

75

00:03:58,329 --> 00:04:04,390

reason for that is because what you did

here is you just define a blueprint, you

77

00:04:04,390 --> 00:04:10,450

are not using the blueprint, so what you

do next is you need to go ahead and use

79

00:04:10,450 --> 00:04:17,530

that blueprint, so which means you

need to call that function, so backspace

81

00:04:17,530 --> 00:04:24,550

to go here to unindent. Indenting

means that you are done with the

83

00:04:24,550 --> 00:04:27,700

function definition so when you start a

new line,

85

00:04:27,700 --> 00:04:32,680

right here that means you are not

writing inside function and so to call a

87

00:04:32,680 --> 00:04:37,840

function what you do is you just call

the name of the function, minutes to hours

89

00:04:37,840 --> 00:04:44,920

and then you open brackets, then inside

brackets you pass a value that you want

91

00:04:44,920 --> 00:04:51,400

to use as input, so let's say you want

70 minutes, you want to convert them to

93

00:04:51,400 --> 00:04:58,510

hours, save the script go and execute

again you don't get any output, but let's see.

95

00:04:58,510 --> 00:05:02,770

As I said you won't get any output,

so why is that?

97

00:05:02,770 --> 00:05:07,630

Well that's because you didn't perform a

print operation there, you didn't call a

99

00:05:07,630 --> 00:05:16,780

print function so what you do is you

print so open brackets close brackets

101

00:05:16,780 --> 00:05:22,630

and inside brackets give the function

code, save your script, go here, execute

103

00:05:22,630 --> 00:05:28,900

and yeah you get the hours, so the

minutes is equal to one point one six

105

00:05:28,900 --> 00:05:37,060

six six hours so it's important to know

that this value here, this is just a

107

00:05:37,060 --> 00:05:44,550

number, so you can see that by doing type.

Execute. Sorry, I didn't print it out.

109

00:05:53,130 --> 00:05:59,530

And so this is a float number, so just a

number. The function gets an input and it

111

00:05:59,530 --> 00:06:04,060

generates an output which is defined by

the hours variable so whatever is

113

00:06:04,060 --> 00:06:10,170

storing the hours variable, that is the

value that the function will output and

115

00:06:10,170 --> 00:06:16,510

yeah, you can do things like you know you

can use this output to do other

117

00:06:16,510 --> 00:06:20,860

operations, let's say you want to add ten

hours there and you want to print that

119

00:06:20,860 --> 00:06:28,210

output, so expect this to be 11.1666.

And so on, and of course

121

00:06:28,210 --> 00:06:34,470

now in your script you can add more

functions if you like, you know like that.

123

00:06:34,470 --> 00:06:40,050

Like seconds to hours. You pass seconds

there

125

00:06:40,050 --> 00:06:47,310

and here seconds.

Return hours and so on and of course this

127

00:06:47,310 --> 00:06:56,639

works separately, so you can say print

seconds to hours and past there actually

129

00:06:56,639 --> 00:07:05,449

we have to change this because this

would be divided by 3600, and let's say

131

00:07:05,449 --> 00:07:14,400

this number of seconds, execute and you get

2.0 hours and you also get the other

133

00:07:14,400 --> 00:07:21,259

output in here and this one here.

Now something important to know is that

135

00:07:21,259 --> 00:07:28,080

these are custom functions and this one

here is also function but this is a

137

00:07:28,080 --> 00:07:33,659

built in function, so constant functions

are functions created by you and built in

139

00:07:33,659 --> 00:07:39,000

functions are functions that are created

by someone else, so in this case print is

141

00:07:39,000 --> 00:07:44,370

created by Python authors and print also

has its own code, but it's more a

143

00:07:44,370 --> 00:07:49,680

low-level code and it's actually

read-only, so you won't be able to see

145

00:07:49,680 --> 00:07:53,669

the code for print. Yeah, this is an

introduction to functions. In the next

147

00:07:53,669 --> 00:07:58,080

lecture I'll show you some more advanced

features of functions, so let's see

149

00:07:58,080 --> 00:08:00,529

you there.

Show less