python递归实现"abcd"字符串全排列

1.保持a不动，动bcd
2.保持b不动，动cd
3.保持c不动，动d

def pailie(head="",string=""):
    if len(string)>1:
        for father_string in string:
            pailie(head+father_string,string.replace(father_string,"")) #关键一点：将头和尾全部传下去
    else:
        print(head+string)


pailie(string="abcd")