数独是一个很好玩的游戏，可以锻炼推理能力。下面的代码可以自动生成数独游戏题目。

from random import shuffle, randrange

def generate():
    # 初始网格
    result = []
    line = list(range(1,10))
    for i in range(9):
        result.append(line)
        line.append(line.pop(0))
        # 注意，这里的切片很重要
        line = line[:]

    # Python允许函数的嵌套定义
    def switchRows(first, second):
        # 这里的括号和换行不是必须的
        # 只是为了方便手机阅读
        (result[first],
         result[second]) =\
         (result[second],
          result[first])

    def switchColumns(first, second):
        for index in range(9):
            (result[index][first],
             result[index][second]) =\
             (result[index][second],
              result[index][first])

    # 随机交换行
    randomRows = list(range(9))
    shuffle(randomRows)
    for i in range(0,7,2):
        switchRows(randomRows[i],\
                   randomRows[i+1])

    # 随机交换列
    randomColumns = list(range(9))
    shuffle(randomColumns)
    for i in range(0,7,2):
        switchColumns(randomColumns[i],\
                      randomColumns[i+1])

   # 随机清空一些格子

    num = randrange(25, 50)
    positions = {(randrange(9),randrange(9))\
                 for i in range(num)}
    for row, col in positions:
        result[row][col] = ' '

    return result

def output(grids):
    print('+'+'-+'*9)
    for row in range(9):
        line = '|'.join(map(str,grids[row]))
        line = line.join(['|']*2)
        print(line)
        print('+'+'-+'*9)   

grids = generate()
output(grids)

运行结果一：

运行结果二：

运行结果三：