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. Unlike strings, lists are mutable. When the bracket operator appears on the left side of an assignment, it identifies the element of the list that will be assigned. 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.

Lists are represented by boxes with the word ‘list’ outside and the elements of the list inside. test refers to a list with three elements indexed 0, 1 and 2.

The bracket operator can appear anywhere in an expression. When it appears on the left side of an assignment, it changes one of the elements in the list.

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 in lists.

from Thinking in Python

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时间： 2024-12-16 10:07:50

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