初始化矩阵python3

Question

我不知道这是不是一个bug，或者我在数组中得到了* token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?

这是一个错误，还是我得到了__mult__令牌的错误语义？

Answer 1

您多次将相同的引用复制到列表中。这样做：

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