9.2. Lists are mutable¶

The syntax for accessing the elements of a list is the same as for accessing the characters of a string: the bracket operator. The expression inside the brackets specifies the index. Remember that the indices start at 0:

>>> print(cheeses[0])
Cheddar


Unlike strings, lists are mutable because you can change the order of items in a list or reassign an item in a list. When the bracket operator appears on the left side of an assignment, it identifies the element of the list that will be assigned.

Activity: CodeLens Changing an item in a list. (listReassign)

The one-th element of numbers, which used to be 123, is now 5.

You can think of a list as a relationship between indices and elements. This relationship is called a mapping; each index “maps to” one of the elements.

List indices work the same way as string indices:

• Any integer expression can be used as an index.

• If you try to read or write an element that does not exist, you get an IndexError.

• If an index has a negative value, it counts backward from the end of the list.

The in operator also works on lists.