试图修改一个值时，Python的2D列表中有奇怪的behavor [英] Python 2D list has weird behavor when trying to modify a single value

问题描述

可能重复：
  <一href="http://stackoverflow.com/questions/240178/unexpected-feature-in-a-python-list-of-lists">Unexpected在列表中的一个Python列表功能

所以我是比较新的Python和我无法用2D解释工作。

So I am relatively new to Python and I am having trouble working with 2D Lists.

下面是我的code：

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

和这里（格式为便于阅读）的输出：

and here is the output (formatted for readability):

[['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]]

为什么每一行获得分配的价值呢？

Why does every row get assigned the value?

推荐答案

这使得有五个引用到同一个列表列表：

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

data = [[None]*5]*5

使用这样的事情，而不是它创建五个单独的列表：

Use something like this instead which creates five separate lists:

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

现在它做你所期望的：

>>> 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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