[issue25681] Assignment of one element in nested list changes multiple elements

[Emanuel Barry]

Emanuel Barry added the comment:

Another way to fix this would be the following:

>>> l=[[''] * 2 for _ in range(3)]
>>> l
[['', ''], ['', ''], ['', '']]
>>> l[0][1] = "A"
>>> l
[['', 'A'], ['', ''], ['', '']]

The * operator on lists doesn't create new elements, it only adds new references to them. A list comprehension will evaluate the expression each time, while repetition (the * operator) will only evaluate it once.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25681>
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