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Welcome back everyone.

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In this lecture we're going to talk about python lists lists are ordered sequences that can hold a variety

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of object types.

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They use square brackets and commas to separate objects in the list.

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For example here we see a list of five numbers where we have each integer separated by a comma instead

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of square brackets list support indexing and slicing just as we did with strings.

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Lists can be nested and also have a variety of useful methods that been called off of them.

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Let's get started by helping over to the Adam text editor and playing around flips and exploring these

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concepts further.

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OK let's start off by creating a list.

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I'm going to say my list is equal to.

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And then we'll say one two three.

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Something you shouldn't do is use list as your variable name.

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It's really tempting because it's so straightforward but list is actually a built in keyboard in Python

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so don't do this so don't use list you something more unique like my list.

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OK.

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So I set my list equal to 1 2 3.

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Let's go ahead and print out my list save that one Python example at PI.

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And now I see 1 2 3.

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Just like a code for string.

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I can also check the length of a list to see how many items are in my list.

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So when I run this I get back three because there's three items in my list and if I add in maybe some

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more numbers.

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So if I add in a bunch of ones and I run this again then it says hey you have seven items in your list

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so one two three four five six seven.

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OK so that's way you can check the length of the list and see how you can construct the list.

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We should also know is that a list can actually hold mixed data types.

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So for example I could start off with an integer then put in a floating point number and then even put

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in a string like hello.

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And my list is not going to complain at all.

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Python has no problem holding multiple data types inside of lists.

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Integer float string doesn't matter.

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A list can hold it.

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Now indexing and slicing works the exact same way like the strings.

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For example if I wanted to grab Hello off this list.

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Well I just kind of read the index positions 0 1 2.

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So in opposition to the third item in this list is hello so I can say my list.

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Square brackets to.

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And then when I run this I get back hello as the output.

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OK so let's try this with another example say A B C D.

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So see if you can practice grabbing a certain letter from this list.

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Try grepping B.

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So it's kind of over 0 1 pass and 1 and then you get BIAZON boy right here B.

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And then I can also do slicing.

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So let's imagine I wanted to grab.

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Let's go ahead and add one more letter here in this list.

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Let's say I want to grab a b c d.

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That sub list or that slice of the list will I want to start off next to one and then I want to go up

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to but not including the last.

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So that's 0 1 2 3 4.

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So that's slicing the exact same way we used to do it with strings.

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Except now we're operating on a list.

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So in one Python example out pi I get back BCT because I'm starting it in additional 1 and then going

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up to but not including in solution 4.

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So that's going to be B C D or 1 2 and 3 now.

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Begin to cover some basic list methods so I have my list.

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ABC the E.

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Let's imagine I wanted to add an item to this list.

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What I could do is I could just say my list dot append open close parentheses and they just type in

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what I want to append to the very end of the list so I can say Z and I'm going to just print off my

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list here and then when I run this I get back ABC and then Z.

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So what's happening here.

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I'm saying my list is ABC the.

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And then I say OK grab that list and using this append method.

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Add a Z to the end of that list and then print out my list.

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Note that I'm not doing this.

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I'm not reassigning my list to be equal to my list thought append because append actually occurs what's

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known as in place so it doesn't return anything.

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And in fact if you were to run this you would get back none because this is actually it's not returning

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anything to be assigned here.

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Instead we just say my list append and again that sort of return idea will make a lot more sense when

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we create our own functions and own methods.

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But right now just keep that in the back of your mind.

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OK so we just saw how we can append the end of a list.

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What if I wanted to insert maybe somewhere else in the list.

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Well I could just use the insert method and then insert.

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It's going to take two parameters.

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The first one is going to be the index of where you want to insert your item so append only goes the

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end of a list.

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But if you want to put something at another in the expedition's it says the first or zero in next to

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the second.

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You can say index 0 comma and then whatever you want to insert.

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So let's insert that Z there again.

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So here I am saying my list thought.

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Insert 0 0.

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Save that and now when I say my list here.

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Notice now I get back z in the zero position and everything's been shifted over to make that change.

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So that's the difference between insert and append append that will just go to the end of the list insert

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will go wherever you say so.

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So index 0 1 to whatever.

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OK now let's imagine I want to remove things from a list.

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Well I can use the pop method for that so I can say oops my list got pop and then I can pass in the

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in the composition of what I want to remove.

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So if I want to move the first element in the list the index which is 0 then that's going to be a.

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So it's a pop at this exhibition 0 and then that actually returns an item that's popped.

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So it's a popped item is equal to my list the pop.

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So then I'll print my list and then also the pop item and I'm actually going to print my list twice.

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So we'll see.

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Copy and paste that here.

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So what I'm going to do is say create my list.

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Print out my list.

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Pop off the item index zero and save that pop item.

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Then print out what mindless looks like and then print out the pop item so let's see what happens.

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So I get back e b c d e.

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Which makes sense is just printing out that list.

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That's from line 2.

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Then they pop off the item and it saves the pop item.

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And now I've been able to successfully remove in expedition's zero BCT.

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And then when I print out my pop item that return back a by default if you don't supply a number here

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if you just say that pop pop off the last item in the list.

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So when I run this again though this all get back here.

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He has the popped off item.

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So again no exposition I'll pop off the list.

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You can always provide any particular index for this and you want to if I want to pop off an expedition

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3 just from that then it goes 0 1 2 3 and it pops off that for me.

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OK.

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So that's a pen insert and pop.

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The last thing I want you to be aware of is you can actually have nested lists.

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So let's go ahead and create an example of that.

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So I'm going to create a list of say 0 1 2 and I'm going to call this my list 1 and then I'll say my

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list to is three four five and then we'll say Maylis three is 670 and then I'll say megaliths is equal

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to a list of my list on my list too and my list 3.

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Save that and let's print out mega list.

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So I saved that and I'm going to run this and those here now I and that's nested list.

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So I have three items in mega list and each of those items is a list itself.

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So that would mean if I were to check the length of mega list they'll actually just report back three

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not nine because as far as this megaliths is concerned it only has three items in it that each of those

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items has its own other set of three items.

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So just keep that awareness as we talk about Nest lists.

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Now let's imagine I want to grab an item from this list.

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So I want to grab.

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Let's say the number seven.

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How would I do that.

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Well the number 7 is inside of my list 3 which is inside a mega list.

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So the first thing I need to do is actually grab my list three from my list.

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So it's going to be 0 1 2.

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So my list 3 is an expedition too.

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So let's grab that.

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Well say square brackets too off of make list and when to run that now I get back six seven eight.

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So then what I could do is another set of indexing to grab 7.

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So it's going to be at 0 1 so that I pass and one and then I get back just the number seven.

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So notice what's happening here mega list of indexing first for that internal list that I'm indexing

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again for that actual number.

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So this is known as stack indexing with a nested list.

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OK.

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So that's the basics of this.

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Again we talked about nested lists.

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The pop a pen insert methods as well as just how to slice an index from a list.

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OK we'll see you at the next lecture.