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Created on 2019-10-17 14:45 by krnick, last changed 2022-04-11 14:59 by admin. This issue is now closed.
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| msg354844 - (view) | Author: JUN-WEI SONG (krnick) * | Date: 2019-10-17 14:45 | |
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)] |
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| msg354848 - (view) | Author: Serhiy Storchaka (serhiy.storchaka) *  |
Date: 2019-10-17 15:31 | |
It is already documented. See note 2 at https://docs.python.org/3/library/stdtypes.html#common-sequence-operations. |
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| msg354849 - (view) | Author: JUN-WEI SONG (krnick) * | Date: 2019-10-17 15:42 | |
sorry that I did not notice it already documented |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:59:21 | admin | set | github: 82688 |
| 2019-10-17 15:42:20 | krnick | set | status: open -> closed resolution: duplicate messages: + msg354849 stage: resolved |
| 2019-10-17 15:31:01 | serhiy.storchaka | set | nosy:
+ serhiy.storchaka messages: + msg354848 |
| 2019-10-17 14:45:11 | krnick | create | |