python-3.x - 初始化矩阵python3

Question

我不知道这是否是一个错误，或者我得到了数组中 * 标记的错误语义：

>>> arr = [None] * 5    # Initialize array of 5 'None' items
>>> arr
[None, None, None, None, None]
>>> arr[2] = "banana"
>>> arr
[None, None, 'banana', None, None]
>>> # right?
... 
>>> mx = [ [None] * 3 ] * 2     # initialize a 3x2 matrix with 'None' items
>>> mx
[[None, None, None], [None, None, None]]
>>> # so far, so good, but then:
... 
>>> mx[0][0] = "banana"
>>> mx
[['banana', None, None], ['banana', None, None]]
>>> # Huh?

__mult__这是一个错误，还是我得到了错误的令牌语义？

Answer 1

您正在多次复制对列表的相同引用。像这样做：

matrix = [[None]*3 for i in range(2)]