尝试修改单个值时，2D 列表有奇怪的行为 [英] 2D list has weird behavor when trying to modify a single value

问题描述

<块引用>

可能的重复:
Python 列表中的意外功能

所以我对 Python 比较陌生，并且在使用 2D 列表时遇到了问题.

这是我的代码:

data = [[无]*5]*5数据[0][0] = '单元格A1'打印数据

这里是输出(为了可读性而格式化):

[['Cell A1', None, None, None, None],['单元格 A1'，无，无，无，无]，['单元格 A1'，无，无，无，无]，['单元格 A1'，无，无，无，无]，['单元格 A1'，无，无，无，无]]

为什么每一行都被赋值?

解决方案

这将创建一个包含五个对相同列表的引用的列表:

data = [[无]*5]*5

使用类似这样的东西来创建五个单独的列表:

<预><代码>>>>数据 = [[无]*5 for _ in range(5)]

现在它可以满足您的期望:

<预><代码>>>>数据[0][0] = '单元格A1'>>>打印数据[['单元格 A1'，无，无，无，无]，[无，无，无，无，无]，[无，无，无，无，无]，[无，无，无，无，无]，[无，无，无，无，无]]

Possible Duplicate:
Unexpected feature in a Python list of lists

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

Here's my code:

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

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]]

Why does every row get assigned the value?

解决方案

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 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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