mat = [[0 for i in range(3)]for i in range(3)]

mat = [False]*(3*3)

print(mat)

>>> mat = [[False]*3]*3
>>> mat
[[False, False, False], [False, False, False], [False, False, False]]
>>> mat[2][1] = True
>>> mat
[[False, True, False], [False, True, False], [False, True, False]]
>>> mat = [[False for i in range(3)] for j in range(3)]
>>> mat[2][1] = True
>>> mat
[[False, False, False], [False, False, False], [False, True, False]]