大一初学者卡在了 python基础题

不懂怎么补充0，不懂如何能够把八个数相加，感觉做不出来了，本人大一初学者

matrix2 = [[2,1,1,1,1],[1,2,1,1,1],[1,1,2,1,1],[1,1,1,2,1],[1,1,1,1,2]]
matrix2_new = [[0] * len(matrix2[0]) for _ in range(len(matrix2))]

for row in range(len(matrix2)):
    for col in range(len(matrix2[row])):
        total = 0
        count = 0
        for i in range(-1, 2):
            for j in range(-1, 2):
                new_row = row + i
                new_col = col + j
                if 0 <= new_row < len(matrix2) and 0 <= new_col < len(matrix2[row]):
                    total += matrix2[new_row][new_col]
                    count += 1
        average = (total-matrix2[row][col])/8
        matrix2_new[row][col] = average

print(matrix2_new)