Data StructuresLesson 9 of 1916 min

Lists

Ordered, changeable collections — the workhorse container of Python.

By the end you will be able to

Create, index, and slice lists
Add and remove items with append, insert, pop, and remove
Sort and reverse lists, in place or into a copy

A list holds many values in order, written in square brackets. Items can be of any type, and — unlike strings — a list can be changed after it is created.

Python

Output

[88, 92, 79, 95, 61]
5
88 61
[92, 79]
— expected output; press Run to execute it yourself

Lists are mutable

You can assign straight into an index, which is the key difference from strings.

Python

Output

['red', 'lime', 'blue']
['amber', 'red', 'lime', 'blue', 'violet']
violet ['amber', 'red', 'lime', 'blue']
['amber', 'red', 'blue']
— expected output; press Run to execute it yourself

Python

Output

[1, 2, [3, 4]]
[1, 2, 3, 4]
[1, 2, 3, 4]
[1, 2, 1, 2]
— expected output; press Run to execute it yourself

Sorting

.sort() reorders the list in place and returns None. sorted() leaves the original alone and returns a new sorted list. Confusing the two is a classic beginner bug.

Python

Output

[61, 79, 88, 92, 95]
[88, 92, 79, 95, 61]
[95, 92, 88, 79, 61]
['Alpha', 'charlie', 'delta']
95 61 415
— expected output; press Run to execute it yourself

Python

Output

[1, 2, 3, 4]
[1, 2, 3, 4] [1, 2, 3, 4, 99]
— expected output; press Run to execute it yourself

Exercise

Write a function top_three(scores) that returns a new list of the three highest scores, highest first. The original list must not be modified.

Python

Output

Press Run to execute this code.

Check your understanding

0/3 answered

1.What does [1, 2, 3].append([4, 5]) produce?
2.What does scores.sort() return?
3.After b = a where a = [1, 2], then b.append(3), what is a?