How to insert 0 into elements of the left and right side of a predetermined two-dimensional integer array (square matrix) **_matrix_**

def mat(matrix, row, col):
for i in range(0, row):
    for j in range(0, col):
        if (i==j):
            print(matrix[i][j], 
                   end = " " );
        else:
            print("0", end = " ");
            
    print(" ");
    
matrix = [[1, 2, 3], 
      [4, 5, 6], 
      [7, 8, 9]];
row = 3;
col = 3;
mat(matrix, row, col);