def matmult(a,b):
zip_b = zip(*b)
# uncomment next line if python 3 :
# zip_b = list(zip_b)
return [[sum(ele_a*ele_b for ele_a, ele_b in zip(row_a, col_b))
for col_b in zip_b] for row_a in a]
x = [[1,2,3],[4,5,6],[7,8,9],[10,11,12]]
y = [[1,2],[1,2],[3,4]]
import numpy as np # I want to check my solution with numpy
mx = np.matrix(x)
my = np.matrix(y)

Result:

>>> matmult(x,y)
[[12, 18], [27, 42], [42, 66], [57, 90]]
>>> mx * my
matrix([[12, 18],
[27, 42],
[42, 66],
[57, 90]])