一个非常棒的递归生成器

#来自《python基础教程》
def flatten(nested):
    try:
        try:
            nested+''
        except TypeError:
            #print('error1')
            print(nested)
            pass
        else:
            raise TypeError
        for sublist in nested:
            for element in flatten(sublist):
                yield element
    except TypeError:
       #print('error2')
        print(nested)
        yield nested

利用递归生成器解决八皇后问题

#冲突检测
def conflict(state,nextX):
    nextY=len(state)
    for i in range(nextY):
        if abs(state[i]-nextX) in (0,nextY-i):
            return True
    return False

def queens(num=8,state=()):
    for pos in range(num):
        if not conflict(state,pos):
            if len(state)==num-1:
                yield (pos,)
            else:
                for result in queens(num,state+(pos,)):
                    yield (pos,)+result
#for t in list(queens()):print(t)
"""
(0, 4, 7, 5, 2, 6, 1, 3)
(0, 5, 7, 2, 6, 3, 1, 4)
(0, 6, 3, 5, 7, 1, 4, 2)
(0, 6, 4, 7, 1, 3, 5, 2)
(1, 3, 5, 7, 2, 0, 6, 4)
(1, 4, 6, 0, 2, 7, 5, 3)
(1, 4, 6, 3, 0, 7, 5, 2)
(1, 5, 0, 6, 3, 7, 2, 4)
(1, 5, 7, 2, 0, 3, 6, 4)
(1, 6, 2, 5, 7, 4, 0, 3)
(1, 6, 4, 7, 0, 3, 5, 2)
(1, 7, 5, 0, 2, 4, 6, 3)
(2, 0, 6, 4, 7, 1, 3, 5)
(2, 4, 1, 7, 0, 6, 3, 5)
(2, 4, 1, 7, 5, 3, 6, 0)
(2, 4, 6, 0, 3, 1, 7, 5)
(2, 4, 7, 3, 0, 6, 1, 5)
(2, 5, 1, 4, 7, 0, 6, 3)
(2, 5, 1, 6, 0, 3, 7, 4)
(2, 5, 1, 6, 4, 0, 7, 3)
(2, 5, 3, 0, 7, 4, 6, 1)
(2, 5, 3, 1, 7, 4, 6, 0)
(2, 5, 7, 0, 3, 6, 4, 1)
(2, 5, 7, 0, 4, 6, 1, 3)
(2, 5, 7, 1, 3, 0, 6, 4)
(2, 6, 1, 7, 4, 0, 3, 5)
(2, 6, 1, 7, 5, 3, 0, 4)
(2, 7, 3, 6, 0, 5, 1, 4)
(3, 0, 4, 7, 1, 6, 2, 5)
(3, 0, 4, 7, 5, 2, 6, 1)
(3, 1, 4, 7, 5, 0, 2, 6)
(3, 1, 6, 2, 5, 7, 0, 4)
(3, 1, 6, 2, 5, 7, 4, 0)
(3, 1, 6, 4, 0, 7, 5, 2)
(3, 1, 7, 4, 6, 0, 2, 5)
(3, 1, 7, 5, 0, 2, 4, 6)
(3, 5, 0, 4, 1, 7, 2, 6)
(3, 5, 7, 1, 6, 0, 2, 4)
(3, 5, 7, 2, 0, 6, 4, 1)
(3, 6, 0, 7, 4, 1, 5, 2)
(3, 6, 2, 7, 1, 4, 0, 5)
(3, 6, 4, 1, 5, 0, 2, 7)
(3, 6, 4, 2, 0, 5, 7, 1)
(3, 7, 0, 2, 5, 1, 6, 4)
(3, 7, 0, 4, 6, 1, 5, 2)
(3, 7, 4, 2, 0, 6, 1, 5)
(4, 0, 3, 5, 7, 1, 6, 2)
(4, 0, 7, 3, 1, 6, 2, 5)
(4, 0, 7, 5, 2, 6, 1, 3)
(4, 1, 3, 5, 7, 2, 0, 6)
(4, 1, 3, 6, 2, 7, 5, 0)
(4, 1, 5, 0, 6, 3, 7, 2)
(4, 1, 7, 0, 3, 6, 2, 5)
(4, 2, 0, 5, 7, 1, 3, 6)
(4, 2, 0, 6, 1, 7, 5, 3)
(4, 2, 7, 3, 6, 0, 5, 1)
(4, 6, 0, 2, 7, 5, 3, 1)
(4, 6, 0, 3, 1, 7, 5, 2)
(4, 6, 1, 3, 7, 0, 2, 5)
(4, 6, 1, 5, 2, 0, 3, 7)
(4, 6, 1, 5, 2, 0, 7, 3)
(4, 6, 3, 0, 2, 7, 5, 1)
(4, 7, 3, 0, 2, 5, 1, 6)
(4, 7, 3, 0, 6, 1, 5, 2)
(5, 0, 4, 1, 7, 2, 6, 3)
(5, 1, 6, 0, 2, 4, 7, 3)
(5, 1, 6, 0, 3, 7, 4, 2)
(5, 2, 0, 6, 4, 7, 1, 3)
(5, 2, 0, 7, 3, 1, 6, 4)
(5, 2, 0, 7, 4, 1, 3, 6)
(5, 2, 4, 6, 0, 3, 1, 7)
(5, 2, 4, 7, 0, 3, 1, 6)
(5, 2, 6, 1, 3, 7, 0, 4)
(5, 2, 6, 1, 7, 4, 0, 3)
(5, 2, 6, 3, 0, 7, 1, 4)
(5, 3, 0, 4, 7, 1, 6, 2)
(5, 3, 1, 7, 4, 6, 0, 2)
(5, 3, 6, 0, 2, 4, 1, 7)
(5, 3, 6, 0, 7, 1, 4, 2)
(5, 7, 1, 3, 0, 6, 4, 2)
(6, 0, 2, 7, 5, 3, 1, 4)
(6, 1, 3, 0, 7, 4, 2, 5)
(6, 1, 5, 2, 0, 3, 7, 4)
(6, 2, 0, 5, 7, 4, 1, 3)
(6, 2, 7, 1, 4, 0, 5, 3)
(6, 3, 1, 4, 7, 0, 2, 5)
(6, 3, 1, 7, 5, 0, 2, 4)
(6, 4, 2, 0, 5, 7, 1, 3)
(7, 1, 3, 0, 6, 4, 2, 5)
(7, 1, 4, 2, 0, 6, 3, 5)
(7, 2, 0, 5, 1, 4, 6, 3)
(7, 3, 0, 2, 5, 1, 6, 4)
len(list(queens()))
92
"""