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All right, so we wanna come
up with a handy function that

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will allow us to display each wish
list in a standard sort of fashion.

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This is, as you know,
a wonderful place to use a function.

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So we want to display our heading, just
like we did here like we say this, books.

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And we also wanna display our list so
we're gonna loop through list.

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So we got this, right?

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Let's make a new function.

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So the function will look like, let's see,

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we're gonna define the new
function called display wish list.

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And first we want to know
what that heading is.

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Let's call that display_name.

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So that'll be books or video games.

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And then the items that we want.

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So we'll just pass in wishes cuz
it's a wish whether it's a book or

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it's a video game list.

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This is the list of there
that we're gonna pass it.

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Awesome.

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So first we'll just print out that header.

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So we''ll say display_name and

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we'll make that a colon.

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There we go You know what, let's go ahead,
let's do this suggested gift thing.

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Let's go ahead and
put this as part of our function.

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Cause we'll suggest a gift
from each one of them.

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So, hm, you know what I was just thinking?

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If we show a suggested gift from the list,

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we shouldn't show it in the other part,
right?

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So I guess what we want to do is we just
wanna pop that first one off, right?

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I mean, what could go wrong?

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So we'll say suggested_gift
equals wishes.pop.

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And we'll get the first one right?

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So we want pop zero.

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Okay, so
let's make this stand out a little bit.

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We'll say print,
we'll add some arrows here at the front.

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Let's really stand out and
we'll print out that suggested_gift.

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And we're removed that from the list.

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So we can probably just
do what we did before.

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So we just wanna loop
through each of the wishes.

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So we can say, for
wish in wishes and we will print.

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Let's see so we used the star before for
bullet, plus wish, there we go,

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and then at the very end let's
just add a blank print here

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after the display wish list, so
that will keep things separate.

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Cool, so now we should be able
to just call that function.

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So we'll say display_wishlist and

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we will call that for
the display name is books.

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And there that wish, the list of
wishes we have that's called books.

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And let's do it for video games.

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So I can just copy this.

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And instead of books,

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we have video games.

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Awesom, that feel pretty clean, right?

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Let's git rid of these other things Here.

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There you go.

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Yeah nice and clean.

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So we've got the two lists,

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we have a function, we're gonna call
it let's see what it looks like.

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So we'll say python Awesome,
looks like we go it.

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I'm gonna scroll this up a little bit and
run that again.

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Sometimes the scrolling
gets a little wacky here.

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Cool, so we've pulled one off and
we pulled the second one off.

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And it looks right, looks good, right?

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There's a little bug
in our program though.

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Let's take a look.

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Do you see what that bug is?

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Here, this'll really demonstrate it.

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Let's do this, I'm gonna go ahead,
I'm gonna call this again one more time.

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That's weird.

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The second time through, it's a little bit
shorter and it's a different suggestion.

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That's because we're changing
the list with that pop command.

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This pop command here is
actually changing this list.

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Now, I made that happen on
purpose to really highlight

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the caution that you should take
when dealing with mutable objects.

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So let's think about how a user
of this function might feel.

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They pass their list in here to get
a function called display wishlist and

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I'm pretty sure that they aren't gonna
expect their list to get an an item

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removed from it.

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That's gonna come as a shock.

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So remember, these parameters can be
thought of like applying the label,

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display name equals books and
wishes equals books.

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So we've applied a label to
that object that was passed in.

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Now, the label only lasts while the
function is running and then it's removed.

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But during that function execution,
the label,

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wishes, it's referring to the same object.

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Now in this case,
it was the video games list.

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That's why when we call pop, it changes
the object because it's the same object.

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So there are better ways to do this.

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One rule to follow is to not
modify someone else's objects

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unless you are explicit about
it in your method name.

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If you find yourself needing to change
a list, like we did here just for

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display purposes,
you can use the copy method.

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The copy method on lists allows
you to make a copy of the list and

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this leaves the previous one intact.

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So let's go ahead and do that.

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So I'm going to make a new copy of
the list when we come in here and

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I'm gonna call it items.

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So items equals wishes.copy.

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Not.copy and then instead of wishes here,
I'm gonna say items.

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And then we can say for item and

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items, item.

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So items is now a completely
unrelated copy of wishes.

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Now, I can change items all I want and
it won't change this, just a copy.

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So here watch, we'll run it again and
you'll see both of them.

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It stayed the same each time.

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It didn't change that
master video games list.

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Now I should point out that you could
actually solve this problem that we're

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having here by not removing
the element from the list at all.

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And only iterating through the lists
starting at the second element.

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You could use what is known as a slice.

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We'll get to that here in a bit, and check
the teacher's notes for a sneak peek.

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Another thing that I want you to be
careful of is loops, and mutability.

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So let's pop open a repel really quick.

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Let's pop open, we'll say python

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Let's take an example from one of
those video games I was playing.

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Let's use Zelda.

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It's an adventure game,
and you collect items, and

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you keep them in your inventory.

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So a typical inventory might
look something like this.

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So we have inventory, do a list and
you might have a shield,

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definitely have apples that's
how you go ahead and eat things.

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And then you have a sword, maybe you'll
have a bow like for a bow and arrow,

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a boomerang.

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All right, basic inventory
from an adventure game, right?

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So one thing that we haven't looked at yet

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is that you can remove
an element from a list by value.

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So you could say inventory.

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And there is a method called remove and

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let's say that we wanted
to get rid of that apple.

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So we're gonna remove the apple
from our inventory and

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now if you look at inventory,
you'll see that it's gone.

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A common problem that happens
is that you mutate the list

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while you're looping over it.

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Like for instance,

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let's say that you wanted to drop
everything from your inventory.

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You might think that you could
do something like this, for item

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in inventory, so we're just gonna loop
though every single one of these items.

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And, we'll say, inventory.remove, and
we are going to remove that item.

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That seems like it make sense, right?

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But we were looping over it, so
what happens is you get this weird

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unexpected result, you still got
a sword and a boomerang left.

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So again,
this is where copy saves the day.

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You just loop over a copy of the array,
like so.

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Let's do this.
So let's come up here.

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Let's reset our inventory.

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Here we go and for an inventory.copy, so
we'll loop through each one of those and

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then we'll choose,
I'm using the up arrow here.

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We'll remove from the master list.

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So this will create a new list,
we're not gonna assign it to a variable,

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it's just gonna create a new one and
it's gonna loop through that.

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But we're gonna remove from
the actual inventory list.

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Now if we take a look, bam.

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So just remember to be extra thoughtful
when dealing with mutable objects.

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After a quick break let's head back and
I wanna show off some pretty great string

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methods that are gonna help dealing
with iterables like our list.