排列算法例子

class Permutation:
    def __init__(self, justalist):
        self._data = justalist[:]
        self._sofar = []
    def __iter__(self):
        return self.next()
    def next(self):
        for elem in self._data:
            if elem not in self._sofar:
                self._sofar.append(elem)
                if len(self._sofar) == len(self._data):
                    yield self._sofar[:]
                else:
                    for v in self.next():
                        yield v
                self._sofar.pop()

a=[1,2,3,4]
for i in Permutation(a):
    print i


    刚刚从看到的，很不错，用到了yield和generator的东西，值得借鉴。