from copy import deepcopy

if not M or not M[0]: return [[]]

row, col = len(M), len(M[0])

res = deepcopy(M)

for x in range(row):

for y in range(col):

temp = [M[i][j] for i in [x - 1, x, x + 1] for j in [y - 1, y, y + 1] if \

0 <= i < row and 0 <= j < col]

res[x][y] = sum(temp) // len(temp)

return res