[MUSIC]

One of the most common things to do with lists is to loop or

iterate through every item.

Now, typically we iterate through each value and

then run some code against that item.

Now, the most common way to do this is with a for-in loop.

We can use the for-in loop because the list is iterable.

That is, it's able to be iterated.

Let's take a look at this ability in the REBEL.

Okay, so let's take a look at this meeting.py file in interactive mode.

So we'll kick this off, python -i meeting.py.

And we have an attendees list.

Remember?

So we have our attendees here.

And this is something we can iterate over.

And the syntax is pretty clean.

It's four and in our case the thing is attendee.

And this will be the variable that our item is stored in for each iteration.

And then the key word, in, and then our list, which is again, attendees.

And then we need to do a colon to start the block.

And then we can work with each one of these items cuz they're already

stored in the attendee variable.

So, let's just print it out.

So I'll say print(attendee).

Awesome.

So, I just want you to imagine that each time through the loop that this variable,

this attendee here is set to the next item from here.

So it just goes one through each right?

So it goes, Ken, Alena, Trevor, Ashley, James.

And just sets that attendee each time through the loop.

Now, here's something that you might not expect.

The last value is actually still available with that label

even after the loop is done.

So if I just type attendee here,

you'll see that's set to the last thing we looped through.

So attendee is still set.

I'm not sure you'll ever need that, but you never know.

One more think while we're here in the REBEL, the end keyword.

Just like how you can use it to see if a string is inside another string, or

we can also use it to see if one item is in the list like for instance.

I can see if actually Ashley was in our list.

I will just say hey, is Ashley in attendees?

True she is, awesome.

So let's pop out of this and let's switch over.

To our wish list file.

So I was thinking how about we make this show every one of the items in our

wish list.

Let's just do the entire list.

So, let's see, so we'll say, let's make a little header here.

So we'll do ("Books:"), and we'll say for book, that's our thing,

in books:, so that's gonna loop through each one of this will be set.

That'll be the book, that'll be the book, that'll be that book, right?

And so, I wanna make sure that this is on 4, space is 4 here.

Don't forget that.

Here we go.

For booking book,so now we want to print them.

And let's do a little bullet, we will do a little asterisks there.

You could use some Unicode magic if you wanted to.

So we'll look through each one of these and then print out the books, cool.

Let's go ahead, let's save that and then run it.

So python -i wishlist.py.

Awesome, beautiful, you know what while I'm here

id like to add another type of product to my wish list.

So my other addiction is video games I've added my wish list from a couple days ago

to the teachers note so lets just copy and paste that.

Paste that up here.

So there we go video games.

Breath of a Wild, wish I was playing right now.

And things don't stay on this list very long.

Confession I've already bought all these video games.

I'm a little bit obsessed.

They're all so good.

Anyways, let's just display my outdated list.

So I think I'd like to do the same thing, I'd like to add a title and

then do a layout, I suppose I could just copy and paste the code, but

mine don't repeat yourself my dry spidey sense is going off.

I don't wanna duplicate that code,

now what if I want to change the way it's displayed,

I have to do that in two places so here let's solve that problem with a function.

So how about I make a function that expects parameters of the display name?

You know, like, is it a book or a video game, and also the list.

Let's do that.

But first, let's take a quick break, because I want to show you the gotchas

surround the passing a mutable object, like a list around.

Take a quick break, and come back refreshed and

we'll tackle this mutability issue head on.