all input arrays must have the same dimensions - python using append

import numpy as np

x = [1,2,3,4] y = [[5,6,7,8],[9,0,1,2]]

j = np.append(x,y,axis=0)

Traceback (most recent call last): File "", line 1, in File "C:\Python27\lib\site-packages\numpy\lib\function_base.py", line 5147, in append return concatenate((arr, values), axis=axis) ValueError: all the input arrays must have same number of dimensions