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Hello and welcome to this video functions are an important part of programming in Python.

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They help us keep our programs organized and makes it possible for us to reuse the code we write.

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There is a principle in software development which all good programmers tried to follow.

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It is called DRY principle D R Y which stands for don't repeat yourself.

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In other words it means don't write the same code twice.

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Now functions can help you avoid writing the same code twice.

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So what are functions functions are basically a collection of computer code which can be executed anywhere

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in your program and also use over and over again.

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So they are reusable and these block of code always do something specific.

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The beauty about functions is that they are reusable.

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The execute or run when they are called and you usually call them by their name.

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So when you create a function in order to activate it you need to run it or call it by the name you

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have given it.

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They can have parameters parameters are basically variables that you define inside a function parentheses

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and also they can have arguments.

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Arguments are the actual value that you give to the function when you call the function.

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They can return data as a result.

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So if you want the functions to return data they can also do that.

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Functions are built in and they can also be cost Tom created.

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Example of the built in functions we have use so far is print.

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The print is a function which allows you to print stuff on the console.

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You can also create your own custom functions which are called user defined functions.

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Creating a function is fairly straightforward.

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Before you create a function it's good to think of a descriptive name that you want your function to

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have.

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The naming convention for a function is the same as in naming convention for variables to create a function.

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You start with the D If keyword which indicates you are about to create a function and then you give

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the function a name followed by parentheses and then the call on the colon basically tells the Python

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interpreter that you're about to start a new line of code.

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So whatever code you write here is the block of code that gets executed when the function is activated.

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When you define functions inside the parenthesis the parenthesis can be empty or you can passing what

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is known as parameters.

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Parameters are basically variables that you define inside the function.

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When you activate your function you can also give it a value that matches the parameter you set.

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That value is referred to as an argument.

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So I've already got a directory.

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I'm just gonna right click on the directory click on new and click on python file.

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I'm going to call it functions and it will automatically append it with a dot P Why file extensions

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are click Okay.

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That was created the file called functions got P Y create a function you start with the keyword d e

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f you do space and then you give the function a name.

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I'm going to call my function sum and then you add the parent.

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This is inside the parent theses.

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You can add parameters or you can leave the parentheses empty.

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So I'm going to add a couple of parameters which are variables I'm going to call this X I'll do a comma

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and I'll call this Y.

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Once you're done you add a call on the column.

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Basically tells Python that you want to start a new line of code.

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So here now is what is called the function body.

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This is the code that will execute when the function is activated.

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So I'm just going to say X plus why.

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So that is it.

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We have created a function.

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Now the X and Y are known as parameters.

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Okay.

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So when this function activates it will print the value of x plus the value of y.

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Once you have created your function the function does nothing until the function is activated.

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Now the process of activating the function is called calling the function.

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It also has other names you can call it execute in the function or invoking the function.

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So any phrase you hear relating to call running execute in invoking they all mean the same thing.

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And when you call it function you call it by its name and you add the parentheses.

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Now if you have defined some parameters during the function definition then you need to parse seen some

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arguments when you core the function those arguments are the values that you give for the parameters

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you have set in the function definition.

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So to activate or call this function that we've created we need to call it by his name and the name

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is sum.

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So say some and then we had the parentheses.

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Now notice that we had two parameters defined inside the function.

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We've got X and Y.

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So now we need to supply the values for x and y those values are known as arguments.

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So if I say for comma five and that basically cause the function parsing those two values for the para

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methods I have set and then it will execute the function.

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So let me save that and then play the file so I click on play and you can see here is return the value

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of nine.

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Okay.

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So is added because here I've said print x plus y.

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So when I call the function are posting two values for 4 x and 5 for y and then returned the value of

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9.

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So that's how you call a function.

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Once you have defined the function it is good to know the difference between parameter and argument.

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Sometimes this can confuse begin as a parameter is actually like a variable that you define inside the

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functions parentheses while an argument is the actual value that you pass or give to the function when

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you call the function.

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So in our function x and y are the parameters while the number 4 and 5 are the actual arguments for

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those parameters.

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So that's it for this video.

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Thanks for watching.

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Bye for now.