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Welcome to today's bonus example.

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In this session, we will be creating a function which gets some numbers from a text file and returns

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the average of those numbers.

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So please create an empty python file and in the same directory with your file.

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Create a file directory.

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So files and bonus 11 dot P are in the same directory inside files please create.

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A text file.

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So just a file with a name, dot, dot, text.

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And there you can write temperatures.

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And just write some dummy.

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Values like that.

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So that is our data file and we want to calculate the average of those numbers.

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And this is our file text file.

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So I'll have these data text file splits on the right so I can see both my codes and the data just for

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convenience.

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Let's start to write a function.

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As you know, we start to define it with def keywords and give a name to the function.

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Usually I like to name functions with a get, so that's when I call them.

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Down here, I can write a variable which represents the returned value of that function.

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So the name average makes sense.

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And now this is like the process.

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So I'll get the average from that process.

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So the naming makes sense.

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I think.

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Right gets average.

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First of all, we want to get the content of that file.

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Here, you want to be careful with the file path.

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So.

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Bonus 11/8 in the same directory with files.

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Therefore, we can say files here and then slash.

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And then dot, dot, dot, txt.

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We want to open that file in red mode as file.

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And read the data with file that read lines.

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So since we are interested to get all these as separate values, then we think about using read lines

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instead of read.

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Read would give us that entire texts as one single string, but this will give us that as a list of

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strings.

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So with that I can indent so that the file is open and then it's closed.

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So at this point I have the data in here.

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I don't need to work on the file anymore, so I indent, but I'm still indented under the function definition.

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Everything is inside the function definition body.

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So if I return the data at this point just to test things out and then I print the average average at

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this point is just the list.

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So let's check it out.

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Run Bonus 11.

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Yeah, that's what we get.

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So it's good to take things step by step.

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See the output.

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And then try to improve it.

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Especially when you are a beginner, you don't want to get overwhelmed by just writing a long list of

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code lines.

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Then you check the output and something doesn't work, and then it's hard to pinpoint the exact error.

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So my suggestion is to create values as we did here.

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Check it out if the value is correctly stored and so on.

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So now we can go ahead and do the next step, which is to remove this item.

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So that is the header of the text file.

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Right.

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And we want to calculate, calculate the average on the numbers.

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But this is a problem.

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So how do we remove that?

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Well, you could apply here.

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List slicing.

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So that is a list, right?

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That is the list.

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Therefore, this syntax makes sense.

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So that is the equivalent of.

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Doing.

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One, two, three.

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Then you get for example, you get from one to the end of the list and that will give you only two and

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three.

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So the item with index zero, which is this item here, is excluded from the list, only the item with

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index one which is declared in here.

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So only the item with index one and everything after that is included in the slides.

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We can do the same in here.

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One like that rather the codes.

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And yeah, now we get only the numbers.

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But I would suggest you not to do that slicing in there or both.

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You exit the file operations and just create a new variable.

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So values is equal to data, and then you extract the values from the data and then return values here

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and you get this the same output.

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So there you have an intermediate variable.

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It's better to have intermediate variables because it helps you debug your programs easier.

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So you know that at this step you're simply reading the data.

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Then at this step you are slicing them.

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So that is better than doing everything in one line, reading and slicing better to have everything

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separated.

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Next.

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You see that these are strings, so we need them as numbers.

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How do you modify all the items of a list?

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Try to think about that.

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Well, using a list comprehension.

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You say floats eye for eye in values.

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So every item will be the float representation of itself for all the items in values.

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So that is the existing list.

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And we use the same variable to store the new lists in that existing variable.

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So we update the value of that variable.

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The new value will be the updated list, run the script and there we have a list of numbers.

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I didn't use integer because these are continuous values, even though none of them is a decimal number.

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I know that these are temperatures and with temperatures you theoretically you could have five points

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one so you could have decimal numbers.

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Therefore it makes sense to use a float data type to represent these values.

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So now we have a list.

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And next.

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We calculate the average.

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The average is the sum divided by the number of items.

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So the sum of the numbers divided by the amount of numbers we have, we can get the sum using the sum

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function.

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It's a built in function and it gets a list as input.

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So the list in our case is values.

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And we divide the sum by the length of values.

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In other words, this would be like we make the sum of them, which is 34, and then we divide that

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by four.

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That gives us the average, and then we turn the average here.

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We do have this underline.

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It says that this shadow's the name average from the outer scope.

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So we can change these to average local.

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But it's better to change it.

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If you are on par charm, it is better to right click here, go to refactor, go to rename and say average

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local and that will change all the occurrences of that variable in the code.

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So you see that par charm knows that this is a local variable, so it will change the local variable

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within the function.

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It does not change that global variable there.

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So press enter and there you have it.

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So that's a local variable.

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It's returned in here.

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Then we get that return value.

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We store it in this global variable and we print that out that value.

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So run this.

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And that's the average of those values.

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So that's a neat function to get the values from a text file and give you the output.

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Thanks for following this and I'll talk to you later.