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In this lecture, I show you how to use functions, which is an excellent way by which you can improve

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your organization of the program, will designed functions make the program easier to use?

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Of course.

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Right.

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And to maintain two functions allow you to split the logic of your problem into smaller chunks.

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And we'll be using quite a few of them in the sections that follow.

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Let me show you a few simple examples to help you get started with functions.

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So let's say that you would like to add two numbers together.

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We've already seen this type of operation many, many times earlier.

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We also learned about fireboats so we can have things such as number one and number two.

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Let's give it a couple of numbers and then you can say no one has two and you get an answer back.

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Now we're setting the parameters of a program.

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Another thing that we can do is the next level of parameterization is to create a simple function that

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has a single job, and that is to add two numbers.

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So to create a function, we use the death or the reserved Caywood and then we provide a name for our

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function, let's call it addition.

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And then inside parentheses, we provide one of zero actually or more parameters.

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You could write a function that doesn't take any parameters, so it would be defined with an empty set

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of parameters.

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In our case, we need two numbers in order to have an addition.

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So one can say in one command number two for the second parameter and to finish the definition, we

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use the colon symbol inside the block of the new function to use a simple print statement which just

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adds the two numbers.

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Just like that, all right, now we have a function defined and to use it, we simply call it name,

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I just press the case.

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So code completion worked and I need to pass in the appropriate number of parameters.

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If I do pass anything, I'm getting an error message.

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And you can see that Python knows that we need to pass in two parameters.

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Try again.

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This time I'm going to pass number two and number four for these two parameters.

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And there is the answer comes back.

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So I called the addition function, which performed the calculation and then printed out the result.

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Let's do a little variation of the functional scenarios that I use, the print function and inside the

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print function, I perform the calculation.

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But very often what you'll be doing is that your function will contain several steps of processing and

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then in the end you will want to return the result of those several steps of processing to whoever made

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the call for the function.

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And that means that we need to introduce at this point the return key word.

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So I'm going to redefine my additional function like this.

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I'm still expecting to receive the two parameters and there's my colon symbol.

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Now inside, I'm going to create a new variable called result, and in it I'm going to store the result

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of the addition between the number one and the number two.

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And then once the result is calculated and ready, I'm going to use the return key word to send it back

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to whoever made the call to the addition function.

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I'm just saying return result and that's it.

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Now, when I call the function, just call it without the print statement, I just kind of hit the up

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error actually to go.

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That's work.

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So I'm just going to type in the edition.

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Name of the function and pass a couple of numbers to say two or three.

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You see that the result comes back is five.

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Now, the result was because of the function call.

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It was not printed by the function itself.

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The result was sent back to the caller, which was this line of code right here.

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And it was printed out because I'm working on the show.

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If you were doing this in such a program, you would need to use the print command so it would look

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like this.

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And the results would come back like that.

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So this is the result of the command coming back with the value that was calculated by the addition

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function and then sent back to the print function by the return statement.

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Another thing that you can do with functions is instead of using anonymous parameters, you can use

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named parameters.

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And that also gives you the opportunity to set defaults and also to make it possible for the user to

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not provide a parameter if a default is present.

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So I'll show you an example.

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We're going to redefine addiction, but this time I'm going to have numb with a default value.

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Now I've got a name for the perimeter and I've got a different value and I'm going to do a good story.

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They should have been number one.

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And I'm also going to have a number two.

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And again, I'm going to have one as the default for number two.

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And then inside I'm going to create the result variable of thing number one, two and three can result.

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All right.

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Now I'm going to.

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Copy the print command, but I'm not going to pass any parameters and see what happens.

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OK, it worked.

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So the result is two, which is what one plus one gives us, it means that the addition function did

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not find any use of parameters, so it just went with its default.

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Another thing that you can do now, because we have defaults and we've got named Parramatta's, is that

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we can go and do something like this.

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And number two equals three.

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Notice that I have not included a parameter for number one and I'm just using this notation.

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Number two equals three instead of just simply passing a number.

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Right.

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So let's go for two equals three, and that will give us four.

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So addition, does the default one for number one.

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And then it used my user parameter for name to which was three.

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Of course, you can still override the defaults by.

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Providing both addition sanction parameters like this.

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OK, so that's about it with an introduction to functions.

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Now you are ready to move on to the next lecture where we talk about classes and objects.