#100DaysOfCode in Python Transcripts
Chapter: Days 7-9: Python Data Structures
Lecture: Manipulating Lists
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Lists are actually pretty simple.
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They're probably one of the things you're
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going to deal with the most in your Python journey
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and the easiest way to demonstrate it is
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to just create one right here of numbers.
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So let's create a stereotypical list, all right.
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We do that by using the square brackets
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and we're going to create five entries in that list.
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So this list contains five items.
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Okay. Now, because we're dealing with numbers specifically,
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we don't have to put the quotes around it, okay.
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If we were dealing with strings that's what we do,
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but we're dealing with just numbers
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so let's just leave it plain like that.
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So that's our numlist.
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We'll just call it back so you can see what it looks like.
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There you go.
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So it's now a list of five numbers, okay.
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1, 2, 3, 4, 5.
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One of the cool things you can do
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with a list is you can actually reverse it.
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Okay.
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So, now need to write some nifty code
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that will go through, parse it,
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and put all the values in back to front.
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We can just do numlist.reverse()
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Call numlist back and there you go,
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5, 4, 3, 2, 1.
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Now we can do that again.
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Okay, and we're back to one, two, three, four, five.
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Now, if we actually go back,
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one thing we can do, is we can actually sort the list.
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So numlist.sort(), okay.
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And there you go 1, 2, 3, 4, 5 again.
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And this is very handy because you can actually sort
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with letters as well.
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Now let's say we want to actually print out all
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of the values inside num list.
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How do we do that?
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We can use a four loop, okay?
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So we can go four num in numlist, print(str(num)).
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So we hit enter and there are our five numbers,
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1, 2, 3, 4, 5
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So it's pretty powerful.
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There's with just this basic ideology you can get a lot
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of stuff done in Python code.
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Now one of the other ways you can actually create a list is
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to call the list function against a certain string.
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Let's say we have a string called -
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we have a variable called mystring.
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And we assign it to string Julian.
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Okay, so mystring is Julian.
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Well how do we convert that into a list?
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We simply call list against it.
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So list(mystring) is Julian.
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And there you go, you see my name has just been chopped up
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so that each letter, or each character I should say,
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is now a string value inside this list.
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Right. So, what can we do?
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We can assign that so l = list(mystring).
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So we're assigning this here to the variable l, alright.
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And we'll just call that back.
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And it's Julian.
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Now what are some interesting things we can do with this?
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Well, there's actually quite a lot.
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We can actually reference the values
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by their position, by their index, inside that list.
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So we can go l[0] is J.
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We can go l[4] is A.
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You can see we got J there, we got A there.
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Very handy.
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What else can we do?
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Well there are a few other functions we can call here.
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We can go pop, and what pop will do it's actually going
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to return the last letter from this list.
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So, the letter N is going to be returned.
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But at the same time,
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it's going to be removed from the list.
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So my name is now Julia.
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Right.
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We can then insert it back in.
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And we use insert for that.
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Now when we insert, we actually,
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if you look at this tool tip here that's cheating,
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you can see we have to specify an index and then the object.
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So what position are we inserting the letter N
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into this list?
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Well, we're going to insert it into position 0,
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1, 2, 3, 4, and 5
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5 is going to be on the end, so position five.
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And what are we inserting?
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We're inserting the letter N.
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All right, it's an actual string.
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Now when we call the list, there we go,
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it's rebuilt with the letter N.
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Another interesting this we can do is
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we can actually replace any of these with any other letter.
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So we can go l[0], which we know will actually return J,
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but we can replace J.
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So L[0] is going to be B.
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So, l is now Bulian.
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Okay?
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Ya, a little play on words.
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Let's go with that.
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Now if we wanted to get rid of the B,
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we could actually delete it or we could pop it.
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The difference is, as I've said before,
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pop will return the letter in that position,
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where as now with the delete option
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it will actually delete it.
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You won't even know what you're deleting.
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It doesn't return anything, it just deletes.
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So if we want to delete that zero we just have
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to type del(l[0]
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and there's the B gone.
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All right?
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Next we can do l.insert().
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We'll choose index position zero.
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And this time we'll put an M in.
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l is now Mulian, okay.
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And now, even better, with pop,
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let's say we do want to return something, we can go l.pop(),
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but now we can actually specify a position, an index.
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So we can go l.pop(0), we get the M returned,
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and the M has also been removed
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from position 0 in the list.
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So those are some cool little nifty tricks
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you can keep up your sleeve, add them to your book,
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because when it comes to lists, you'll end up dealing
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with them quite a lot.
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So knowing how to pop and how to delete and insert
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and append, which is another one I'll show you quickly.
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l.append(), let's add S.
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We can append, append will always add right at the end
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into the last position.
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So definitely keep all of these handy.
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You'll be using them quite a lot.
