如何在Python中生成列表的所有排列

Question

如何在Python中生成列表的所有排列

如何在Python中生成列表的所有排列，与该列表中的元素类型无关？

例如：

permutations([])

[]

permutations([1])

[1]

permutations([1, 2])

[1, 2]

[2, 1]

permutations([1, 2, 3])

[1, 2, 3]

[1, 3, 2]

[2, 1, 3]

[2, 3, 1]

[3, 1, 2]

[3, 2, 1]

Answer 1

以下代码仅适用于Python 2.6及更高版本一，进口itertools：import itertools排列（订单事宜）：print list(itertools.permutations([1,2,3,4], 2))[(1, 2), (1, 3), (1, 4),(2, 1), (2, 3), (2, 4),(3, 1), (3, 2), (3, 4),(4, 1), (4, 2), (4, 3)]组合（顺序无关紧要）：print list(itertools.combinations('123', 2))[('1', '2'), ('1', '3'), ('2', '3')]笛卡尔积（有几个迭代）：print list(itertools.product([1,2,3], [4,5,6]))[(1, 4), (1, 5), (1, 6),(2, 4), (2, 5), (2, 6),(3, 4), (3, 5), (3, 6)]笛卡儿积（一个可迭代的本身）：print list(itertools.product([1,2], repeat=3))[(1, 1, 1), (1, 1, 2), (1, 2, 1), (1, 2, 2),(2, 1, 1), (2, 1, 2), (2, 2, 1), (2, 2, 2)]

Answer 2

def permutations(head, tail=''):     if len(head) == 0: print tail    else:         for i in range(len(head)):             permutations(head[0:i] + head[i+1:], tail+head[i])称为：permutations('abc')