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Something to point out is that when your

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function doesn't have a return statement, save, execute,

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it implicitly returns a None object.

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None is a specific object

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in Python, which means nothing.

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It's not an integer, it's not

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a float, it's not a string.

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It's just None.

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It means nothing.

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So Python, what it does is, if

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it doesn't find the return statement on

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the background, it does this return None.

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So if you execute that oops, an indentation error.

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That's a good thing. So you see that all this block here

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has to be the same level of indentation.

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If you indented four lines here, you have

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to indent four lines in here, too.

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So indentation has to be consistent.

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That looks right.

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So we got the same output None here and None there.

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Some people do this mistake.

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Instead of returning, they use print.

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Instead of using return, they use a print

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function, the_mean, which works half the way.

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So it still returns the value,

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and it also returns None.

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So what's going on here is that when you call

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the function here, Python will execute all these lines.

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So it calculates the_mean.

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Then it goes to the next line.

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So line by line, it will print the_mean.

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So it will print out the_mean in here,

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and then it will look for a return statement.

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It doesn't find it, so it will return None.

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The problem with this is that if you try to do

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some other operations with your mean value, let's say mymean

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is equal to the mean function 0, 3, and 4, okay?

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And I want to print out mymean + 10.

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So I would expect that this would give me the

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value of, 7 is the sum divided by three.

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So 2 point something plus 10, 12 point something.

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But let's see what this will give me.

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[No audio]

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So this will give me a TypeError

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instead. It tried to add the none type, which is None.

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So this is a none type.

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That's the type of this value.

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It's trying to add that to ten.

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So mymean is None, because it returns none.

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And the interpreter will try to add up that to 10.

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That's not possible.

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So that's why you shouldn't use print.

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If I replace that with return instead, remove the

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parentheses, save, execute, that will give me 12.3.

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That is the average plus ten.

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However, this doesn't mean you cannot

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use print in your functions.

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You can actually do that.

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Let's say you just want to print some information.

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[Author typing]

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started, Function started!, and execute that.

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So you get the output of print in

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here, and then Python returns the mean.

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So you get the mean, you store it

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in here, the output of your function.

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But the value of the function is

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always what you return in here.

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So if you see that it,

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[Author typing]

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so always use return in your

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functions, unless you have a very special reason to do so.

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[Outro sound]