Getting Things From Lists¶

One cool thing about lists is that you can grab certain items from the list by using slices or indicies. You don’t really need to remember those terms, but there are two things you should remember:

1. The first item in the list isn’t 1, it’s 0.
2. We get the item in the list that we want using [].

For example:

>>> [1, 2, 3, 4][0]
1

This way looks a little goofy and confusing, so let’s assign the list to a variable.

>>> favorite_numbers = [1, 2, 3, 4]
>>> favorite_numbers[0]
1

Neat!

We can also get a portion of things from a list:

>>> favorite_numbers = [1, 2, 3, 4]
>>> favorite_numbers[0:2]
[1, 2]

Wait a second. We’ve asked for the items in the list from 0 to 2. The value at index 0 is 1, the value at index 1 is 2, and the value at index 2 is 3. So why did we only get [1, 2] back?

This is because the slice sytax (the way we get just a portion of items from a list) returns the first item in the slice up to, but not including the second value. Tricky.

What about getting things a single item from a list within a list? Remember our list of things and PyCon feelings?

>>> more_things = [things, pycon_feelings]
>>> more_things
[[5, True, 'hello'], ['Hooray', 'Good', 'Amazing', 'Lacking bees']]

How do we get True from the list things in more_things? Well, what does this give us?

>>> more_things[0]

It gives us the list things, since that’s what’s at index 0. Can we build on more_things[0] to get the second item in in _that_ list?

>>> more_things[0][1]
True

Awesome!

Modifying Lists¶

One last topic on lists: changing them.

You can add to a list like this:

>>> my_list = ["lions", "tigers", "bears"]
>>> my_list
['lions', 'tigers', 'bears']
>>> my_list.append("Oh my")
>>> my_list
['lions', 'tigers', 'bears', 'Oh my']

You can remove items a couple of ways.

You can remove a specific item by its value:

>>> my_list.remove("lions")
>>> my_list
['tigers', 'bears', 'Oh my']

You can remove and return the last item in the list using pop:

>>> my_list.pop()
'Oh my'
>>> my_list
['tigers', 'bears']

And you can remove and return an item by its index:

>>> my_list.pop(0)
'tigers'
>>> my_list
['bears']

More List Exercises¶

$ python3.6 capital_guesser.py
What is the capital of Montana? Helena
Yay! Great job!
$ python3.6 capital_guesser.py
What is the capital of Georgia? Sacramento
Sorry, that's incorrect.

proteins = ["ham", "turkey", "beef", "tofu"]
condiments = ["mustard", "mayo", "hummus"]
veggies = ["tomato", "lettuce", "onion", "sprouts"]
breads = ["white bread", "wheat bread", "pita bread", "sourdough"]

$ python3.6 lazy_chef.py
The Terminator has turkey, lettuce, and mayo on rye bread.
The First Lady has tofu, tomato, and hummus on pita bread.
The San Diegan has tuna, sprouts, and dill spread on sourdough.