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You have completed Introducing Lists!
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Now that we can add stuff, we'll definitely want to make sure we can get stuff out of the list. Let's explore `del` and `pop`.
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books = [
"Learning Python: Powerful Object-Oriented Programming - Mark Lutz",
"Automate the Boring Stuff with Python: Practical Programming for Total Beginners - Al Sweigart",
"Python for Data Analysis - Wes McKinney",
"Fluent Python: Clear, Concise, and Effective Programming - Luciano Ramalho",
"Python for Kids: A Playful Introduction To Programming - Jason R. Briggs",
"Hello Web App: Learn How to Build a Web App - Tracy Osborn",
]
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All right, so I've updated our master
list, it's in the teacher's notes.
0:00
I'm gonna go ahead and copy it, and
paste it, so it's all written now.
0:04
Here we go,
we have the Learning Python book first.
0:09
Let's remind ourselves of
what our app here is doing.
0:12
So I'm going to go to python -i,
for interactive mode,
0:15
and open up wishlist, right.
0:19
It's pulling the first book out,
it's printing the first item out.
0:22
But I've already read that book.
0:25
So I kind of want this off my wish
list before someone buys me an extra
0:27
copy of it.
0:30
I wanna remove it, so you might have
not seen the del statement before.
0:31
Well, basically del which is short for
0:36
delete allows you to essentially
remove a label from an object.
0:38
It deletes the name not the object.
0:44
So let's go ahead and use my delicious
lunch as an analogy one more time.
0:47
So, let's create a new
variable called Craig's lunch.
0:52
And we'll set the value to
the Unicode value of a taco,
0:57
more in the teacher's notes about Unicode.
1:02
So, to do that,
we're gonna use a named Unicode value.
1:05
So, we're gonna say backslash capital N,
and then a curly brace, and
1:08
the name of the Unicode object is taco,
that's what we want there.
1:12
So if you look at this,
you can see a beautiful taco, there it is.
1:17
Now, my taco left overs
are labeled with craigs_lunch,
1:23
but I have a bunch of other
leftovers in the office fridge here.
1:29
So, I also wanna label the type of meat.
1:32
Now, these tacos that I made last night,
they are carne asada.
1:35
So I'm gonna add an additional label.
1:39
So I'm going to say
carne_asada = craigs_lunch and
1:40
we'll see that carne_asada now
also points to that same taco.
1:47
Both of these labels are on that taco,
they are referring to the same object.
1:54
I can remove one of the labels by using
the del keyword, so let's remove my lunch,
2:00
so scary, del craigs_lunch.
2:06
And now you'll see if I type craigs-lunch,
2:10
we get name error because it
doesn't know what's going on.
2:13
It's like, what is craigs_lunch?
2:17
I don't know what it is, cuz I deleted,
I removed the label, now the label's gone.
2:19
But don't fear, my tacos still exist
under my old label of carne_asada.
2:23
That's still around and there is my taco.
2:28
Now, if I remove this label,
2:32
our office manager Molly will come through
and do a quick clean up of the fridge.
2:35
Anything without a label
gets garbage collected and
2:39
it's thrown out,
since no one that's claiming it.
2:42
More in the teachers note about how
garbage collection works in Python.
2:44
List indices work very similar to this,
that is,
2:48
that you can think of them as labels.
2:51
So, I can use the del keyword to
delete an item at a certain index.
2:53
But it is really just deleting the label,
not the actual object.
2:59
Now, for example,
3:03
I definitely don't want this first
book on my personal wish list, right?
3:04
This Learning Python book,
I don't want it on my wish list, but
3:08
I do wanna recommend it still.
3:11
So I'll add a new variable,
called, let's clear this up here.
3:12
So, I'll create a new variable called
recommendation and I'm going to
3:16
go ahead and add a label to
that object of recommendation.
3:21
So now it's got two labels,
it's got book[0] and recommendation,
3:26
and now I can run a del
statement on book[0].
3:31
And if you take a look at books,
you'll see that Learning Python
3:34
is no longer there, but
my variable still has access to it.
3:40
There is the Learning Python
that I've pulled out.
3:45
And sometimes, you don't want
to keep the value around, right?
3:47
You want it to be garbage collected.
3:49
That is when del is a perfect choice,
it's great.
3:51
Often times though,
3:54
you don't want to do a removal from
the list, you wanna keep it in a variable.
3:55
And when this is what you want,
pop is the list method for you.
3:59
By default, if you just use pop,
it takes the last item from the list.
4:03
So if we say books, and
that method is called pop().
4:08
We're gonna pop the last item off there,
so we should get Hello Web App back.
4:12
Now, see how the last item was returned?
4:16
The repl printed it out, right?
4:18
So I could have stored that in a variable.
4:20
This style of removing the last item
is often referred to as LIFO, or
4:23
last in first out, right?
4:27
The last item that's added to the list is
the first one that comes out when you pop.
4:30
Now you can also pop at a specific index.
4:34
So if I wanted to say books.pop(0)
it will pop the first book up,
4:37
so automate the boring stuff and
I look at books it's not there.
4:43
And there we go,
number one in my wish list.
4:47
I think I'm gonna buy this right now,
my wish has been granted.
4:49
Great job getting items added,
inserted, and
4:54
remove from a list. How are things feeling?
4:56
Remember, if anything at all has you
perplexed, you are part of a wonderful
4:59
community of fellow students,
they would love to chat with you.
5:03
You could even pop a question off
that unanswered question list, and
5:06
answer one for your classmates.
5:09
So, now that we can manipulate
these lists, I think it's time
5:11
to start taking a look at some typical
solutions that they provide, sound good?
5:14
Let's talk through some common use
cases of this powerful data type,
5:19
right after this quick break
5:22
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