数独判断是否合法：如何验证对角线元素是否重复？

def verify_line(self, board, x, y):    for i in range(9):        if board[i][y] == board[x][y] and i != x:            return False        if board[x][i] == board[x][y] and i != y:            return False    if x == y or x + y == 8:        for k in range(9):            if board[k][k] == board[x][y] and k != x:                return False            if board[k][8 - k] == board[x][y]:                if k != x and k - 8 != x:                    return False    return True