double square brackets side by side in python

Question

I\'m completely new at Python and have an assignment coming up. The professor has asked that we look at examples of users coding Pascal\'s Triangle in Python for something t

Answer 1

Square brackets are used to define lists, but also to get things from lists.

When you have a list of lists and want something from an inner list, you need to get that inner list (using brackets) and then get the desired thing inside (using brackets again).

lol = [[1, 2, 3], [4, 5, 6]]
lol[1]
# [4, 5, 6]
lol[1][0]
# 4

Answer 2

If you have a list

l = ["foo", "bar", "buz"]

Then l[0] is "foo", l[1] is "bar", l[2] is buz.

Similarly you could have a list in it instead of strings.

l = [ [1,2,3], "bar", "buz"]

Now l[0] is [1,2,3].

What if you want to access the second item in that list of numbers? You could say:

l[0][1]

l[0] first gets you the list, then [1] picks out the second number in it. That's why you have "square bracket next to square bracket".