Functions - The basics |Section 3|Celestial Warrior

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Hi again, in this video you'll learn how

to create a function in Python and how

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to use that function, so let me go ahead

and create a script. Let me name this my

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function.py and let's go ahead and

create a function. Creating a function

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will always begin with the DEF keyword

which is, which means define. Now that is

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followed by the name of the function, so

you need to give your function a name

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let me name this minutes to hours and

as you may guess already what I'm

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creating is a function that will convert

minutes to hours, so you create the

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procedure on how to convert minutes to

hours and then you can call that

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procedure, so you can call that function.

You can give that function any values

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when you call it and the function will

produce an output depending on the value

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and depending on the formula, on the

procedures that you write in here, so

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let's go ahead and do that, minutes

to hours. Now functions normally they have

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some input and they produce some output.

The input goes inside these brackets

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here. In our case the input could be

minutes so this is just a variable, you

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can give it any name that you want, you

can give it any name that you want for

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the function name as well, so the input

is minutes and then the output will be

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

Here what to do you always choose a

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column, press enter and that will be auto

indented, so as you see the functions

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everything that you write below the

first line of a function definition is

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indented and every line after that, so the

DEF keyword, the name of function, the

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input and here we write the body of the

function. What we want to do is let's

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say variable house equals to

minutes / 60 that should give us the

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hours. Note that if you are on Python 2

you want to do 60 point zero because

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if you do that you get an integer as

an output, not a float, so in

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Python 2 you have to explicitly pass

a float when you do division to get a

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number, to get a float with decimal

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

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

simple function, so this is what the

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function will perform and then the last

line of the function is normally a

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return keyword, so notice that these are

reserved keywords def and return, and

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what I want to return is, well gets what?

The output which is hours, so that's the

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idea, we are getting minutes. The user

will input a value for that later when

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you call a function and Then minutes

will be divided by 60 and that operation,

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that number will be stored in the hours

variable which is a variable that exists

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only inside the function so this is

called a local variable. If you call it

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outside the function it will not work,

but we'll cover that later. And so then

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we return the value of that variable.

Now I'll save this and open the terminal.

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Make some space there and let me execute

the script. You get nothing and the

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reason for that is because what you did

here is you just define a blueprint, you

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are not using the blueprint, so what you

do next is you need to go ahead and use

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that blueprint, so which means you

need to call that function, so backspace

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to go here to unindent. Indenting

means that you are done with the

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function definition so when you start a

new line,

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right here that means you are not

writing inside function and so to call a

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function what you do is you just call

the name of the function, minutes to hours

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and then you open brackets, then inside

brackets you pass a value that you want

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

70 minutes, you want to convert them to

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hours, save the script go and execute

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

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As I said you won't get any output,

so why is that?

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Well that's because you didn't perform a

print operation there, you didn't call a

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print function so what you do is you

print so open brackets close brackets

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and inside brackets give the function

code, save your script, go here, execute

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and yeah you get the hours, so the

minutes is equal to one point one six

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six six hours so it's important to know

that this value here, this is just a

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number, so you can see that by doing type.

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

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And so this is a float number, so just a

number. The function gets an input and it

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generates an output which is defined by

the hours variable so whatever is

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storing the hours variable, that is the

value that the function will output and

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yeah, you can do things like you know you

can use this output to do other

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operations, let's say you want to add ten

hours there and you want to print that

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output, so expect this to be 11.1666.

And so on, and of course

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now in your script you can add more

functions if you like, you know like that.

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Like seconds to hours. You pass seconds

there

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and here seconds.

Return hours and so on and of course this

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works separately, so you can say print

seconds to hours and past there actually

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we have to change this because this

would be divided by 3600, and let's say

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this number of seconds, execute and you get

2.0 hours and you also get the other

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output in here and this one here.

Now something important to know is that

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these are custom functions and this one

here is also function but this is a

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built in function, so constant functions

are functions created by you and built in

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functions are functions that are created

by someone else, so in this case print is

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created by Python authors and print also

has its own code, but it's more a

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low-level code and it's actually

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

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the code for print. Yeah, this is an

introduction to functions. In the next

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lecture I'll show you some more advanced

features of functions, so let's see

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you there.

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