python多维数组改变元素值的坑？

Question

>>> l=[[0 for i in range(10)] for i in range(10)] >>> l [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> l[0][0]=23 >>> l [[23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> n=[[0]*10 for i in range(10)] >>> n [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> n[0][0]=23 >>> n [[23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> N=[[0]*10]*10 >>> N [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> N[0][0]=23 >>> N [[23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> arr=[0 for i in range(10)] >>> L=[arr for i in range(10)] >>> L [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> L[0][0]=23 >>> L [[23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0], [23, 0, 0, 0, 0, 0, 0, 0, 0, 0]] >>> 为什么l和n能正确修改，L和N修改了每个子列表的首元素值？

Answer 1

因为 l 和 n 生成每个子列表都是不同的；
而 L 和 N 生成的每个子列表，都是相同的，都是指向同一个列表对象；

判断依据，可以通过： id(l[0], l[1]) 看两个子列表地址（l 替换成相应的 N,n,L,l）

另外：

    对于：N = [[0] * 10 ] * 10`
    
    可以理解成：
        1. x = [0] * 10
        2. N = [x * 10]  => 很明显，仅仅将 x 这个对象的引用复制了 10 次而已
        
   而对于：
        arr=[0 for i in range(10)]
        L=[arr for i in range(10)]
        
   这个就更好理解了，遍历那么都次，存的还是同一个索引，这个稍微改下就能正常：
        L=[copy.copy(arr) for i in range(10)]