的Python：初始化空巢列表

Question

怪时列表行为

有人能解释为什么：

b = 10*[[]] 
b[0].append(3) 

B现在是：

[[3], [3], [3], [3], [3], [3], [3], [3], [3], [3]] 

，但如果我这样做：

b = [[] for _ in range(10)] 
b[0].append(3) 

b为现在：

[[3], [], [], [], [], [], [], [], [], []] 

还要注意的是

10*[[]] == [[] for [] in range(10)] 

返回

True 

Answer 1

because: 
    >>> b = 10*[[]] 
    >>> b[0] is b[1] 
    True 
    >>> b = [[] for _ in range(10)] 
    >>> b[0] is b[1] 
    False 
    >>>