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Welcome back.

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In this video, I want to talk about an important concept, which is return.

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It's a key word in Python that we are going to see a lot when working with functions.

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So let's have a look.

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If I let's say I want to create a function called sum, which, by the way, already exists in Python,

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but we're going to create our own and I'm going to say number one for number one.

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And number two, well, our sum function is going to add nine one plus num two, nice and simple function.

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Now, if I run some with number four and five, guess what's about to happen?

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I'm going to hit run.

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And nothing happens, which I mean, might not be surprising to you, because we're not printing anything,

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right.

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But what if I run print here?

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Will this change?

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Let's see.

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Hmm, I get none.

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Is that what you expected and we've seen none before.

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Right, I mean, remember when we had a list, let's say one to three, and then we did something like

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clear on it?

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In our Ed, it gave us this little arrow and said none, and we talked about this idea of on lists,

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something like clear changes the actual list and clears everything and empties the list.

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But it doesn't return a new list.

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It just modifies the existing list, but instead just returns none to us.

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Well, functions are just like that.

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They always have to return something.

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And when they don't return anything like there's no return keyword here, it automatically returns none.

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So if we don't have something like return here, it's always going to return nothing.

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But if we add return, it's going to say as soon as we get to, like, to hey.

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I want you to exit this function, and when you exit this function, I want you to return whatever this

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expression gives us, if I click, run.

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If we change this to 10.

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Plus five, we get 15.

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And this is a good general rule with functions, because functions can do two things right?

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One, it can return something.

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So at the end of the function, whatever, after the function gets run, we return something either

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Nunn or some sort of a value, some sort of a data type, or we can have a function that doesn't return

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anything but perhaps modifies something.

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So, for example, I could print.

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And if I had run here.

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I return none because I don't have that return statement, however, my function does something it modifies.

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Well, the look of this tax, right, a prince high for us.

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So a function either modifies something in our program or returns something.

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And this is a topic that is quite advanced that we'll get into later on when we talk about functional

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programming, but a good rule of thumb with functions is this a function should do one thing really

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well.

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And usually a function should return something.

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Now, this doesn't mean that any function that maybe does multiple things or any function that doesn't

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return something is bad, but it's generally good practice to make your code simple and readable, to

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have these two rules.

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For example, here, if I have print and addition, will, this function is doing multiple things.

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It's worrying about printing and it's also worrying about something.

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And the definition this function is called some.

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I mean, if I didn't know or I didn't see this and all I did was run some, I think having printing

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high would be surprising because the name doesn't really describe what it does.

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I mean, I'm expecting this to be some time.

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Why is my program saying hi?

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So we want to make sure that our function does one thing and one thing only really?

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Well, because as we'll see later on, we can combine and run different functions together.

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And then also we want to make sure that we return something, because this way, what we can do is we

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can actually assign this return value to a variable.

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For example, I can say total equals to some 10.

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And because this function returns something and when it's done, running is going to have 15 as a value,

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that's the same thing as what we're doing here.

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And here's the cool part now I can run maybe some 10.

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Plus total.

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Now, let's go through this one by one.

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I define my function, the Python interpreter is going to say, all right, I know what some is now

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you've defined it.

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I'm going to keep it in memory.

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It's going to keep going, keep going until line seven.

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And it's going to say, hey, I want a variable total and I want that total variable to equal some 10

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five.

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And before we even assign anything to total python, interpreter is going to say some what?

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Some again.

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Oh, I remember here.

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It's in memory, OK, at some I'm going to give it arguments 10 and five.

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So it's going to go run that function.

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As soon as we end this closing bracket, it's going to go into the sun.

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It's going to say, hey, no one is going to equal ten.

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Hey, number two is going to equal five.

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Now we go to line two and it's going to say, hey, I want you to add ten plus five because I know what

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these variables are.

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And then once you're done with that and this turns into 15, I want you to return.

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So the Python interpreter, finally, when it's done calling some, is going to say, hey, assign the

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value of 15 to the variable total and then it's going to go to the next line.

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Hey, I want to print something.

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What do you want to print?

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Well, I want to print this.

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It's going to say, hey, what some I know what's on this.

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I have it in memory.

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And then again, it's going to say ten.

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And then the next argument is going to be total.

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Hey, what's total?

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Let me go memory and find out.

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Oh, it's 15.

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So it's like saying 50.

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And this is the power of functions, right, I'm able to return things and assign them to variables

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and call them like this and I can keep running them if I want to.

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If I want to make this even simpler, I can go.

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Some instead of total will be right here.

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And look at that now.

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I have it all in one line and if I click run.

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Again, it's still works.

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OK, but what if we do something like this?

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What if I say define some and then I'll say define inside of here another function and this function

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takes number one and number two.

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And in here, we finally return number one and number two.

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Hmm, let's test this out.

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What do you think will happen?

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Well, first, let's say total equals some 10 plus 20.

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And then I'm going to print total.

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If I click, run.

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Now, why is that and this should be obvious to you, because here I'm saying, hey, I want you to

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define something and what are we going to do with the function?

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Some well, inside of here, I'm going to define another function.

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But this return statement is actually not run.

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Right, because all we're doing inside of this block, this code block.

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Is this part we're defining the function, but we're never calling another function.

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So this returns none.

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And we've lost the ability to well, to call this function.

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So how can we solve this?

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One way is to return, right?

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So at the end here, we have to make sure that the indentation is right and we're going to return another

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func.

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So let's add return and see what happens here.

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If I click, run.

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All right, I get this function now, so total is going to equal this function that we returned and

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it's in memory.

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OK, but I'm not getting the result that I want, right?

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And why is that?

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Because while we're not calling this function so there's a few ways that we can do this.

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We can either give it the parameters or the arguments in here.

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So let's say 10, 20.

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And if I click, run.

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I get 30 or if we want to keep whatever we give it here, I can just simply say another funk.

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So if we give it number one and number two and I click run.

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Hey, look at that, I get 30.

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Now, this video you might have to watch over and over, because it does stretch your mind a little

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bit, and to be honest, this function is not very good because it's well, it's very confusing.

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Your function should be easy to understand.

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So we might want to change this up a bit, maybe instead over here of having the same parameter names

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just to clarify it.

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Maybe we can say and one and and two.

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And then here we do.

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And one plus and two to clarify that when we return this other function, I'm using the parameters,

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number one, and number two that we called here.

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Because this definition of a function doesn't really care what these things are.

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It only cares when another function gets called.

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Now, if you need to pause the video and look at this and maybe practice this a little bit, that's

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completely understandable.

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But I wanted to show you the power of return.

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You can have nested functions just like you could with conditionals, but you have to be careful that

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your function either returns something, otherwise it's going to return none.

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And most of the time you're going to want to return something from a function so we can do something

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like this where we assign it to a variable so we can use it later on in our programs.

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I'll see you in the next one by.

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One last thing, a return key word automatically exits the function so that in here, if I added another

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piece of code like print, hello?

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Or maybe even have return five in here, you see that it's still valid, but if I run this.

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I still get 30 because the interpreter never gets to line five and six, because as soon as we return

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something from a function, it exits that function.

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And the reason that this part doesn't exit the function is because, remember, inside of this function,

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we're defining.

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So we're not actually running this part.

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We're just saying, hey, when we see another function coming up in our code, we know what it is,

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but we're not going to run it.

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So it's going to look like this.

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And as soon as it sees the return statement, when it gets cold, it's going to say, all right, I'm

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exiting out of this function with this value.

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Just a little heads up.