Python：使用递归算法作为生成器

def getPermutations(string, prefix=""):    if len(string) == 1:        yield prefix + string    else:        for i in xrange(len(string)): for perm in getPermutations(string[:i] + string[i+1:], prefix+string[i]):     yield perm

或没有累加器：

def getPermutations(string):    if len(string) == 1:        yield string    else:        for i in xrange(len(string)): for perm in getPermutations(string[:i] + string[i+1:]):     yield string[i] + perm