python 实现把一维的序列循环赋值给二维的序列问题，求助

Question

python 实现把一维的序列循环赋值给二维的序列问题，求助a = [0,0,0,0]b = []for i in range(4):a[3] = ib.append(a)print b想实现的是：[[0, 0, 0, 0], [0, 0, 0, 1], [0, 0, 0, 2], [0, 0, 0, 3]]可是实际是：[[0, 0, 0, 3], [0, 0, 0, 3], [0, 0, 0, 3], [0, 0, 0, 3]]求问哪里有问题？