파이썬 코딩 도장

col, row = map(int, input().split())

matrix = []
for i in range(row):
    matrix.append(list(input()))

import copy
count = 0
b=copy.deepcopy(matrix)
for i in range(row):
    for j in range(col):
        if matrix[i][j]=="*":
            continue
        else:
            matrix[i][j]==int(0)
            for k in range(i-1,i+2):
                for y in range(j-1,j+2):
                    if (matrix[k][y]=="*"):
                        matrix[i][j]+=1
                    else:
                        continue

print(matrix)

이렇게 코딩을 짜 보았는데, 

Traceback (most recent call last):

  File "/Users/dungdi/Desktop/python/main.py", line 124, in <module>

    matrix[i][j]+=1

TypeError: can only concatenate str (not "int") to str

이러한 오류가 떴습니다. 뭐가 문제였던걸까요?