python - 为什么 python 在这里复制列表？

Question

我有一个函数，应该表示“3D”数组中的一个立方体，但其中一层中间有一个正方形。 IE。

def cube(n):
    list1 = []
    list2 = []
    list3 = []


    for a in range(n+2):
        list3.append(str('c'))
    for b in range(n+2):
        list2.append(list(list3))
    for c in range(n+2):
        list1.append(list(list2))


    for d in range(1,n+1):
        for e in range(1,n+1):
            list1[0][d][e]='h'
    return list1

pprint.pprint(cube(2))

>>>

[[['c', 'c', 'c', 'c'],
['c', 'h', 'h', 'c'],
['c', 'h', 'h', 'c'],
['c', 'c', 'c', 'c']],

[['c', 'c', 'c', 'c'],
['c', 'h', 'h', 'c'],
['c', 'h', 'h', 'c'],
['c', 'c', 'c', 'c']],

[['c', 'c', 'c', 'c'],
['c', 'h', 'h', 'c'],
['c', 'h', 'h', 'c'],
['c', 'c', 'c', 'c']],

[['c', 'c', 'c', 'c'],
['c', 'h', 'h', 'c'],
['c', 'h', 'h', 'c'],
['c', 'c', 'c', 'c']]]

但我想要这个:

>>>

[[['c', 'c', 'c', 'c'],
['c', 'h', 'h', 'c'],
['c', 'h', 'h', 'c'],
['c', 'c', 'c', 'c']],

[['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c']],

[['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c']],

[['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c'],
['c', 'c', 'c', 'c']]]

仅第一层中的 h。为什么Python要这样做？

Answer 1

这里有一个最小的改变来获得你想要的。首先添加

from copy import deepcopy

然后替换:

list1.append(list(list2))

与:

list1.append(deepcopy(list2))