尝试修改单个值时，二维列表具有怪异的行为 [英] 2D list has weird behavor when trying to modify a single value

问题描述

可能重复:
Python列表列表中的意外功能

Possible Duplicate:
Unexpected feature in a Python list of lists

所以我对Python还是比较陌生，在处理2D列表时遇到了麻烦.

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

这是我的代码:

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

这是输出(为便于阅读而设置):

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]]

为什么为每一行分配值?

Why does every row get assigned the value?

推荐答案

这将创建一个包含对相同列表的五个引用的列表:

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

data = [[None]*5]*5

使用类似这样的方法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)]

现在它可以满足您的期望:

Now it does what you expect:

>>> 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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