python3创建二维数组_python3 二维数组

关于python3创建二维数组的问题

做题时遇到创建数组时遇到一个小问题，如下：

grid=[
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]]
seen=[[0]*len(grid[0]) for _ in range(len(grid))]
print(seen)
seen[0][0]=1
print(seen)

a=[[0]*len(grid[0])]*len(grid)
print(a)
a[0][0]=1
print(a)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

输出结果如下：

[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[1, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[1, 0, 0, 0, 0], [1, 0, 0, 0, 0], [1, 0, 0, 0, 0], [1, 0, 0, 0, 0]]

可见第一种创建数组的方法是正确的，而第二种给一个元素赋值，对应的所有行相同列都会赋值。

总结

创建一个4*5的二维数组正确格式如下：

ls=[[0]*5 for _ in range(4)]
1

而以下面这种方式创建二维数组时赋值会出现错误：

ls=[[0]*5]*4
1