Python 列表乘法:[[...]]*3 生成 3 个在修改时相互镜像的列表 [英] Python list multiplication: [[...]]*3 makes 3 lists which mirror each other when modified

问题描述

为什么会这样?我真的不明白:

<预><代码>>>>P = [ [()]*3 ]*3>>>磷[[(), (), ()], [(), (), ()], [(), (), ()]]>>>P[0][0]=1>>>磷[[1, (), ()], [1, (), ()], [1, (), ()]]

解决方案

您对同一个列表进行了 3 次引用.

<预><代码>>>>a = b = []>>>a.追加(42)>>>乙[42]

你想这样做:

P = [[()] * 3 for x in range(3)]

Why this is happening? I don't really understand:

>>> P = [ [()]*3 ]*3
>>> P
[[(), (), ()], [(), (), ()], [(), (), ()]]
>>> P[0][0]=1
>>> P
[[1, (), ()], [1, (), ()], [1, (), ()]]

解决方案

You've made 3 references to the same list.

>>> a = b = []
>>> a.append(42)
>>> b
[42]

You want to do this:

P = [[()] * 3 for x in range(3)]

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