8.2: Lists are mutable
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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) 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.
>>> numbers = [17, 123] >>> numbers = 5 >>> print(numbers) [17, 5]
The one-eth 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
- If an index has a negative value, it counts backward from the end of the list.
in operator also works on lists.
>>> cheeses = ['Cheddar', 'Edam', 'Gouda'] >>> 'Edam' in cheeses True >>> 'Brie' in cheeses False