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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 but

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we're going to create our own.

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And I'm going to say number one for number one and number two.

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Well are some function is going to add name one plus name 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 I'm going to hit run and nothing

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happens.

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Which I mean might not be surprising to you because we're not printing anything 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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I get none.

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Is that what you expected.

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And we've seen none before.

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Right.

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I mean remember when we had a list let's say one two three and then we did something like clear on it

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in our editor it gave us this little arrow and said none and we talked about this idea of on lists something

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like clear changes the actual list and clears everything and empties the list but it doesn't return

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a new list it just modifies the existing list but instead just returns None to us.

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Well functions are just like that they always have to return something and when they don't return anything

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like there's no return keyword here it automatically returns None so if we don't have something like

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return here it's always going to return nothing but if we add return it's going to say as soon as we

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get to lying to hate I want you to exit this function and when you exit this function I want you to

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return whatever this expression gives us.

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If I click Run I get nine if we change this to 10 plus five we get 15 and this is a good general rule

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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 none or

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

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but perhaps modifies something.

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So for example I could print

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and if I hit run here I return None because I don't have that return statement.

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However my function does something it modifies Well the look of this tax write a prints high for us.

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So a function either modifies something in our program or returns something and this is a topic that

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is quite advanced that we'll get into later on when we talk about functional programming.

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But a good rule of thumb with functions is this a function should do one thing really well and usually

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a function should return something Now this doesn't mean that any function that maybe does multiple

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things or any function that doesn't return something is bad but it's generally good practice to make

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your code simple and readable to have these two rules.

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For example here if I have print and additions.

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Well this function is doing multiple things.

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It's worrying about printing.

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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 high

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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 summed.

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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 well because as we

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will 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 can

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actually assign this return value to a variable.

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For example I can say total equals to some 10 5 and because this function returns something and when

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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.

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Now I can run maybe some 10 plus total.

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Now let's go through this one by one I define my function the Python interpreter is going to say all

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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 7.

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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 5.

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And before we even assign anything to total Python interpreter is going to say some.

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What's some again.

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Oh I remember here it's in memory OK at some.

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I'm gonna give it argument's 10 and five.

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So it's going to go run that function as soon as we end this closing bracket.

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It's going to go into the sum it's going to say Hey Number one is going to equal 10.

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Hey num 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 10 plus five because I know what these

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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 value of

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15 to the variable total.

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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.

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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 10 and then the next argument is going to be total Hey what's total.

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Let me go in memory and find out oh it's 15.

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So it's like saying 15 and this is the power of functions right.

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I'm able to return things and assign them to variables and call them like this and I can keep running

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them if I wanted to if I want to make this even simpler I can go some instead of total.

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We'll be right here and look at that.

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Now I have it all in one line and if I click run again it still works OK.

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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.

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Another function and this function takes num 1 and num to an end here we finally return number one and

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number two.

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Let's test the set.

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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 and then I'm going to print Total if I click Run I

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get none now.

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Why is that.

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And this should be obvious to you.

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Because here I'm saying hey I want you to define some.

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And what are we going to do with the function some.

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Well inside of here I'm going to define another function.

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But this return statement is actually not run right because all we're doing inside of this block this

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code block is this part we're defining the function but we're never calling another function so this

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returns None 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.

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Right.

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So at the end here we have to make sure that the indentation is right.

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And we're going to return another func.

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

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If I click Run All right I get this function now.

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So total is going to equal this function that we returned.

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And it's in memory OK.

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But I'm not getting the result that I want.

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Right.

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And why is that.

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Because while we're not calling this function.

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

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func.

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So if we give it num 1 and num two and I click Run 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 bit.

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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 maybe we can say and one and and two and then here we do and one plus and two to

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clarify that when we return this other function I'm using the parameters number one and number two that

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we called here 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 completely

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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.

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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.

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So we can do something 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 in the next one by

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one last thing a return keyword automatically exits the function so that in here if I added another

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piece of code like print Hello or maybe even have return five in here you see that it's still valid

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but if I run this I still get 30 because the interpreter never gets to line five and six because as

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soon as we return 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 we're just saying hey when we see another function coming up

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in our code we know what it is 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 alright I'm exiting

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out of this function with this value just a little heads up.