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Editorial Team
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Asked: 2026-05-14T15:15:34+00:00

When I try this code: data = [[None]*5]*5 data[0][0] = ‘Cell A1’ The value

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When I try this code:

data = [[None]*5]*5
data[0][0] = 'Cell A1'

The value of data ends up like:

[['Cell A1', None, None, None, None],
 ['Cell A1', None, None, None, None],
 ['Cell A1', None, None, None, None],
 ['Cell A1', None, None, None, None],
 ['Cell A1', None, None, None, None]]

Why does the 'Cell A1' value appear in every nested list?

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1 Answer

  1. Editorial Team

    This makes a list with five references to the same list:

    data = [[None]*5]*5

    Use something like this instead which creates five separate lists:

    >>> data = [[None]*5 for _ in range(5)]

    Now it behaves as expected:

    >>> data[0][0] = 'Cell A1'
>>> print(data)
[['Cell A1', None, None, None, None],
 [None, None, None, None, None],
 [None, None, None, None, None],
 [None, None, None, None, None],
 [None, None, None, None, None]]
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