Nested Lists

An element of a list can be any value, even another list. A list inside a list is called a nested list. Nested lists are useful for data that comes in groups, such as study groups:

study_groups = [["Jennifer", "Boris"], ["David", "Ava", "Nancy"]]
print(study_groups)

This prints:

[['Jennifer', 'Boris'], ['David', 'Ava', 'Nancy']]

The list study_groups has two elements, and each of them is a list of names: one study group. The first index selects a group, which is an ordinary list:

print(study_groups[1])

This prints:

['David', 'Ava', 'Nancy']

To get one student, add a second index in square brackets. study_groups[1][0] first takes the element at index 1 (the second group, ["David", "Ava", "Nancy"]) and then, from that list, the element at index 0:

print(study_groups[1][0])

This prints:

David

Everything you know about lists works for the inner lists too. len(study_groups) is 2, the number of groups, while len(study_groups[1]) is 3, the number of students in the second group. study_groups[0][-1] is the last student of the first group, "Boris". And study_groups[0].append("Tim") adds Tim to the end of the first group.