Python有效数独棋盘检查器9x9验证方块但不显示输出结果

def isValidSudoku(board):
    # 检查每一行
    for i in range(9):
        row = []
        for j in range(9):
            if board[i][j] != '.':
                if board[i][j] in row:
                    return False
                row.append(board[i][j])

    # 检查每一列
    for j in range(9):
        col = []
        for i in range(9):
            if board[i][j] != '.':
                if board[i][j] in col:
                    return False
                col.append(board[i][j])

    # 检查每一个3x3的子网格
    for block in range(9):
        row_start = (block // 3) * 3
        col_start = (block % 3) * 3
        square = []
        for i in range(row_start, row_start + 3):
            for j in range(col_start, col_start + 3):
                if board[i][j] != '.':
                    if board[i][j] in square:
                        return False
                    square.append(board[i][j])

    return True

board = [
    ['5', '3', '.', '.', '7', '.', '.', '.', '.'],
    ['6', '.', '.', '1', '9', '5', '.', '.', '.'],
    ['.', '9', '8', '.', '.', '.', '.', '6', '.'],
    ['8', '.', '.', '.', '6', '.', '.', '.', '3'],
    ['4', '.', '.', '8', '.', '3', '.', '.', '1'],
    ['7', '.', '.', '.', '2', '.', '.', '.', '6'],
    ['.', '6', '.', '.', '.', '.', '2', '8', '.'],
    ['.', '.', '.', '4', '1', '9', '.', '.', '5'],
    ['.', '.', '.', '.', '8', '.', '.', '7', '9']
]

if isValidSudoku(board):
    print("数独棋盘有效")
else:
    print("数独棋盘无效")