递归实现全排列python

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")

与上一个两个不同，一是，第一个a排完顺序后，下一个a不能再排，二是替换的时候不能把重复的也替换掉

def pailie(head="",string=""):
    if len(string)>1:
        for num,father_string in enumerate(string):
            if father_string in string[0:num]:#如果字符与前面的重复说明拍过顺序了
                continue
            pailie(head+father_string,string.replace(father_string,"",1))#只能替换一次
    else:
        print(head+string)

pailie(string="abca")