Python - a two-dimensional array definition

1.

a=[]
arrays=[a*3]

In fact, as arrays[[]]

2.

arrays=[a]*N

It appears to be to create a two-dimensional array, but only creates N pointing to a reference, so once a change, arrays in the N list will change
eg:

a=[]
N=3
arrays=[a]*3
arrays[0].append(1)#看上去只为第一个list添加整数1，实际上---
print(arrays)

Output[[1], [1], [1]]

3.

arrays=[[]for i in range(N)]

eg:

N=3
arrays=[[]for i in range(N)]
print(arrays)

Output[[], [], []]