Iteration

[MUSIC] 0:00 One of the most common things to do with lists is to loop or 0:04 iterate through every item. 0:07 Now, typically we iterate through each value and 0:09 then run some code against that item. 0:12 Now, the most common way to do this is with a for-in loop. 0:14 We can use the for-in loop because the list is iterable. 0:18 That is, it's able to be iterated. 0:22 Let's take a look at this ability in the REBEL. 0:24 Okay, so let's take a look at this meeting.py file in interactive mode. 0:28 So we'll kick this off, python -i meeting.py. 0:33 And we have an attendees list. 0:39 Remember? 0:41 So we have our attendees here. 0:43 And this is something we can iterate over. 0:44 And the syntax is pretty clean. 0:46 It's four and in our case the thing is attendee. 0:49 And this will be the variable that our item is stored in for each iteration. 0:53 And then the key word, in, and then our list, which is again, attendees. 0:58 And then we need to do a colon to start the block. 1:04 And then we can work with each one of these items cuz they're already 1:07 stored in the attendee variable. 1:10 So, let's just print it out. 1:12 So I'll say print(attendee). 1:13 Awesome. 1:18 So, I just want you to imagine that each time through the loop that this variable, 1:20 this attendee here is set to the next item from here. 1:24 So it just goes one through each right? 1:27 So it goes, Ken, Alena, Trevor, Ashley, James. 1:29 And just sets that attendee each time through the loop. 1:31 Now, here's something that you might not expect. 1:34 The last value is actually still available with that label 1:37 even after the loop is done. 1:40 So if I just type attendee here, 1:42 you'll see that's set to the last thing we looped through. 1:43 So attendee is still set. 1:47 I'm not sure you'll ever need that, but you never know. 1:48 One more think while we're here in the REBEL, the end keyword. 1:51 Just like how you can use it to see if a string is inside another string, or 1:55 we can also use it to see if one item is in the list like for instance. 1:59 I can see if actually Ashley was in our list. 2:03 I will just say hey, is Ashley in attendees? 2:04 True she is, awesome. 2:10 So let's pop out of this and let's switch over. 2:12 To our wish list file. 2:15 So I was thinking how about we make this show every one of the items in our 2:20 wish list. 2:24 Let's just do the entire list. 2:26 So, let's see, so we'll say, let's make a little header here. 2:27 So we'll do ("Books:"), and we'll say for book, that's our thing, 2:30 in books:, so that's gonna loop through each one of this will be set. 2:36 That'll be the book, that'll be the book, that'll be that book, right? 2:41 And so, I wanna make sure that this is on 4, space is 4 here. 2:46 Don't forget that. 2:51 Here we go. 2:53 For booking book,so now we want to print them. 2:54 And let's do a little bullet, we will do a little asterisks there. 2:57 You could use some Unicode magic if you wanted to. 3:01 So we'll look through each one of these and then print out the books, cool. 3:05 Let's go ahead, let's save that and then run it. 3:09 So python -i wishlist.py. 3:12 Awesome, beautiful, you know what while I'm here 3:18 id like to add another type of product to my wish list. 3:22 So my other addiction is video games I've added my wish list from a couple days ago 3:25 to the teachers note so lets just copy and paste that. 3:30 Paste that up here. 3:35 So there we go video games. 3:38 Breath of a Wild, wish I was playing right now. 3:41 And things don't stay on this list very long. 3:43 Confession I've already bought all these video games. 3:46 I'm a little bit obsessed. 3:48 They're all so good. 3:49 Anyways, let's just display my outdated list. 3:50 So I think I'd like to do the same thing, I'd like to add a title and 3:52 then do a layout, I suppose I could just copy and paste the code, but 3:57 mine don't repeat yourself my dry spidey sense is going off. 4:02 I don't wanna duplicate that code, 4:06 now what if I want to change the way it's displayed, 4:08 I have to do that in two places so here let's solve that problem with a function. 4:11 So how about I make a function that expects parameters of the display name? 4:16 You know, like, is it a book or a video game, and also the list. 4:20 Let's do that. 4:23 But first, let's take a quick break, because I want to show you the gotchas 4:24 surround the passing a mutable object, like a list around. 4:27 Take a quick break, and come back refreshed and 4:31 we'll tackle this mutability issue head on. 4:33