New submission from JUN-WEI SONG <sungboss2...@gmail.com>:
When I used the nested list, I need to initialize the nested list, so I used this expression: >>> nested_list = [[]] * 5 see also: https://stackoverflow.com/questions/12791501/python-initializing-a-list-of-lists So I later learned that such an expression would make the list inside the list have the same reference, which would cause the problem that you modified one element would lead to all elements changed in the nested list. For example: >>> nested_list[0].append(1) >>> nested_list [[1], [1], [1], [1], [1]] Therefore, maybe we could tell users how to initialize the list on the documentation like below: If you need to initialize the nested list, you could follow the below example, also, be aware of the expression like ``[[]] * 5``, this will cause the five lists in the nested list to have the same reference. >>> nested_list = [[] for _ in range(5)] ---------- assignee: docs@python components: Documentation messages: 354844 nosy: docs@python, krnick priority: normal severity: normal status: open title: Improve the documentation of the nested list initialization type: enhancement versions: Python 3.8 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue38507> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
