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At this point of the program development, we allow the user to add and show to the items.

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The user can also exit the program.

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But in this video, we want to add a new feature, a new edit feature which allows the user to edit

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existing to do items.

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So how do we go about adding a new feature?

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Well, to be able to add a new feature, you should think from the user's perspective.

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So try to be in the user's shoes.

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So let's run the program as it is now and let's think as the user.

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So this says add a type, add show or exit.

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So the first thing we want to do is we want to add here an option.

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Edit.

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So type and show, edit or exit.

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So if we run this now, we're going to get the correct prompt.

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Then the user might want to press.

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Edit Here we want to add a new case to count for that scenario.

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So Case added a column.

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Press Enter pie charm indents automatically the next line.

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And here, What can we write?

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Well, for now, let's just say print.

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Got it.

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Just something dummy and free around the program and try again to think as the user so the user wants

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to press.

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Edit But first they want to add something like add a new to do clean adds through add.

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Prepare.

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And then they want to press.

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Edit So we press.

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Edit got it was printed out.

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So that case statement is working fine, but let's think of how do we want to tell the program which

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of these items we want to edit.

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So in this command line interface, we have basically two options.

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So either we should say that we want to add its clean and we explicitly write, type down the exact

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to the item there, and then the program asks us a second question such as What do you want the new

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to do to be?

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And you write the new to do which will override the existing to do or you just say the number.

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For example, you want another two, so you want to edit number two.

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I think the second scenario where you just tell the number of the to do is more meaningful.

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So you, the user first says show it knows the order of these and then it says number two.

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Edit and then the program asks again the user to enter the new to do for that.

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To override that.

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To do.

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And so on.

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So.

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Let's close this and go to the program.

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So if the user enters.

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EDIT We want to ask the user a new question.

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Let's say number is equal to input.

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Number of the to do to edit.

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So we ask the user to enter the number of the to do item.

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So if the user enters to for example, two will be stored in the number of variables.

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Let's see if we successfully get that.

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So print number run again.

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So let's say edit two and we get out to.

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So what can we do now with this too?

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Well, we will use lists indexing system to be able to extract that item of the list, which has an

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index of two.

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So let me give you an introduction to this list Indexing system.

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Let's say we have the list to dos is equal to clean.

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Through and.

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Prepare.

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So that's the list.

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So if you want to extract that item from the list you do to do square brackets, one that will give

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you a throw, which of course you can also store that in a variable to do is equal to that to do is

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equal to throw.

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And that's the list.

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Again, sorry to dos is the list.

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And to this one gives you a throw.

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Why?

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Because this first item has an index of zero.

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This second item has an index of one.

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And the next item has an index of two and so on.

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So what we're doing here is we are accessing the item with index one, which is the item through.

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So that means if you press zero here, you get clean.

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If you do two, you get prepared.

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If you write three, you will get an error because it says index list.

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Index is out of range, so there are no items with index three.

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So back to our program.

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We get the number.

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So the index.

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And we use that index to access the to do list some number here and that will give us the to do item

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which the user wants to add it.

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And what do we do with this?

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Now, before we answer that question, let's make sure we got this correctly.

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So let's call this existing to do is equal to that and print existing to do.

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Let's see what this is going to give us.

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So I'll run this.

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Let's add a new to do.

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Clean.

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Add the new one.

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Prepare.

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Show the to do list.

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Clean prepare.

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Then press edit to edit a new one number of to do to edit.

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So that is zero.

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That is one.

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But the user doesn't know this, so the user maybe will write down one to mean that.

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So we need to adjust for that in the script.

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We will do that also.

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So let's try to enter one and we get an error.

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The error is in line 16.

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So it's here.

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It says that.

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Type error list indices must be integers or slices, not SDR.

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So it seems that the index is a string.

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What is the index?

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The index is this part here, this number that we give in here.

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But the interpreter is saying this is string and this is true because the input function always, always

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produces a string type.

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So even if the user enters a number, that number is actually a string.

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It is just text.

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It is not recognized by Python as a number.

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So let me show you what I mean by that.

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Let's say you want to store in variable A, you want to store the input, enter a number.

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So you enter a number, let's say ten, right?

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And you might think that A now is a number, right?

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So if you do a plus two, you will get an error because you are trying to concatenate a string.

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So ten is a string.

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You can also see the quotes here with a number that doesn't make sense for Python.

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The interpreter is confused, doesn't know what to do so you get an error.

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The solution here is to use a function which converts a string to a number.

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So that function is int.

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If you write ten here, it will give you a number.

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So let's say B again, is it?

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Ten type B is int, so integer is a whole number in Python.

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You can also use.

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Float.

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Let's say we had this string.

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You press enter and B now is a float.

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So it's a decimal number.

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So float converts strings to decimal numbers and it converts strings to whole numbers.

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So type B is a float.

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Right.

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So we use that to convert this into ints.

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So if you say integer and you wrap that inside end, so the output of the input function will be the

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input of the end function.

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In other words, the output of the input function is one, so one will be the input of the function

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and we get to one as a whole, as an integer, a whole number.

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So we need to work with whole numbers here because indices are all numbers.

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So.

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We had the to do list to do.

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You cannot say 1.3.

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You will get an error.

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You can only say one or two or.

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And so on.

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Right now.

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Number is on it.

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So now we shouldn't get an error anymore.

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So let's run this.

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Ad clean at through show.

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Edit I'll edit number one press enter and we get extracted the through item from that list.

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So number one extracted through.

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But as a user, I don't know about the indexing system of Python.

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I don't know that Python starts the indexing from zero.

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So we also as a programmer, we need to adjust for that.

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Lack of knowledge from the user's part about the system that Python is based on.

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That's an easy solution for that.

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We just go to our script, so we grab the number.

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Let's say the user entered one, but they meant zero, right?

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The first item.

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But the item has an index of zero.

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So we say number is equal to number.

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So one minus one.

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So we get zero if the user enters one.

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One minus one, we get zero.

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If the user enters to two minus one, we get to one answer one.

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Right?

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So that should give us the actual to do that.

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The user wants to add it, but then how do we go about replacing that to do so?

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We have the list to dos now with two dos and.

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One, we got the item.

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But if you want to replace that item, we say to do this one is equal to new item, whatever the user

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enters here.

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Press enter.

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And now if you check to this, you see that flow is replaced with that new item.

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Therefore, we go in here and instead of doing that.

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We see to do number.

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So throw is equal to new.

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To do what is new to do?

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Well, new to do is something we get from the user using again the input function enter new to do.

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So I'll run this now and you'll see that this is working well at clean, at throw at repair.

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Show.

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So we have three items and we want to add it through.

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So we count one, two.

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Oh, that's number two.

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So edit number of the to do, to edit to enter, new to do.

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How about this symbol?

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Press enter press show to see the to dos.

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And here we have disassemble is the item with number two sorry for the type of disassemble anyway exit

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and we exit the program.

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So that's the final version of the edit feature.

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Let me delete this break line.

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So what you learned in this video was how to convert from a string to a number.

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Using that in function, you also learn how to access items from a list using that syntax, and you

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also learn how to replace an item using that syntax.

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This was quite a long video, but these features are very, very crucial for you.

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You're going to use them in every application that you'll build with Python, no matter if it's a web

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development, data science or other fields of Python.

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So thank you for following and I'll talk to you later.