Leetcode: Set Matrix Zeroes @Python

class Solution:
    # @param matrix, a list of lists of integers
    # RETURN NOTHING, MODIFY matrix IN PLACE.
    def setZeroes(self, matrix):
        m=len(matrix)
        if m==0: return None
        n=len(matrix[0])
        first_0_row,first_0_col=False,False
        if matrix[0].count(0)>0: first_0_row=True
        for i in range(m): 
            if matrix[i][0]==0:
                first_0_col=True
                break
        for i in range(1,m):
            for j in range(1,n):
                if matrix[i][j]==0:
                    matrix[0][j]=0
                    matrix[i][0]=0
        for i in range(1,m):
            if matrix[i][0]==0:
                for j in range(1,n):
                    matrix[i][j]=0
        for j in range(1,n):
            if matrix[0][j]==0:
                for i in range(1,m):
                    matrix[i][j]=0
        if first_0_row:
            for i in range(n):
                matrix[0][i]=0
        if first_0_col:
            for j in range(m):
                matrix[j][0]=0