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Great, you can now
create functions, call them,

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and add parameters to
make them more dynamic.

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And now what you can also do is
to make a function return a value.

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So this function, SayHello, is
just a function that does an action.

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It doesn't return anything.

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Now I'm going to create a new function.

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So as you can see, when I just press
Enter here, I still have the indentation.

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So what I'm going to do, I'm going to
remove that indentation and do depth again.

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So let's say I'm going to create
a function, double number.

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And let's say, hey, or just number.

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So you can create as
many functions as you want.

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You just need to put
them one after the other.

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Okay, so now I'm going to create
a function with one parameter.

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And the name of the
function is double number.

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And I simply want to return
the double for this number.

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So I'm first going to compute the
result, which is the double of that number.

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So I'm going to create a variable
result is equal to number times two.

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And then what I'm going to do, I'm
going to use the return statement.

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Return result.

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So what this function
will do when it's called,

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so first it's going to receive
a parameter number.

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It's going to compute the double
of this number and return the result.

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So when you call the function, you can
get the double of the number you send.

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Just before we continue,
one thing I'm going to do here

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is that so we create a variable
and we just return that variable.

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So basically, we are not going to use that.

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We only return that variable.

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So what I can do instead of result is equal
to number times two and return result,

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I can just return number
times two and remove that.

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So this is going to return
directly the correct value.

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And now, well, I can call this function.

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So I'm first going to put a comment here.

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Okay, so we don't call those.

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So this is not a problem.

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You could call this and call this.

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That's not a problem.

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Here, I just want to call
that function and not this one.

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So we just have less lines in the output.

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So what I can do, I can do double number.

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I can use the auto-completion
with, let's say, three.

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Okay.
And I'm going, of course, to store that.

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So let's say number is equal to double
number three and then print number.

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So when you create a function that
returns something with a return statement,

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when you call the
function, you can actually

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assign the value you
get here to a variable.

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And then you can print,
of course, the variable,

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or you can do whatever
you want with the variable.

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So I just run the program
and you can see I have six.

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So the double of three is six.

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So the number variable
here contains the value six.

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All right.
So you can see two types of functions here.

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So those who are just going to do
an action and don't return anything,

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and those who compute or maybe get a value
from somewhere and then return that value.

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Note that you can return
any kind of value you want.

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Here, I return an integer number.

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But you can return a float, a Boolean,
a string, list of whatever you want,

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while just return what
you want from the function.

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But just make sure that
when you call the function,

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you actually know what kind of
data type you are going to get.

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Okay. And one thing
you can also do is you

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can call a function
inside another function.

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And thus, you can really make
functions as building blocks

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that allow you to create
even more building blocks.

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Let's see that with an example.

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Def print double number.

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So with number, and
I'm going to do result is

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equal to double number of the
number we get here, and then print result.

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Or maybe make it better.

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So double of plus the
number casted as a string, plus

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is, and then plus the result
also casted as a string.

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So when you call this
function, what it's going

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to do is going to call the
double number function.

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Okay. So from the function,
you call another function.

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And you can see this parameter I got here,

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I'm going to pass it also to
the double number function.

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And then I can print some stuff
with the parameter and the result I got.

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And I'm going to call it
this print double number.

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I'm going to remove that.

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And I'm going to remove that.

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And I'm simply going to run.

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And you can see double of three is six.

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Okay. It's all happening in that function.

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So here you have a function that
just does an action and that's it.

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Here, a function that returns a number.

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And here, a function
that does an action, but

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inside, you actually
call another function.

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And you can create
another function that is

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going to call that one,
et cetera, et cetera.