写一个函数，输出字符串中字符的字典

import random

lst=['a','b','c']
t=['a','a','a']

def nextch(c):
    if c in lst:
        i=lst.index(c)
        if  i==len(lst):
            return lst[0]
        else:
            return lst[i+1]
        
def nextlist(l):
    if l:
        newlist = l[:-1]
    else:
        return []

    if l[-1] == lst[-1]:
        newlist = nextlist(l[:-1])
        newlist.append(lst[0])
        return newlist
    else:
        newlist.append(nextch(l[-1]))
        return newlist
        
r = random.randint(0,len(lst)**3-1)
print 'r is %s' % r
for i in range(len(lst)**3+r):
    print 't is %s' % t
    t=nextlist(t)

r is 18
t is ['a', 'a', 'a']
t is ['a', 'a', 'b']
t is ['a', 'a', 'c']
t is ['a', 'b', 'a']
t is ['a', 'b', 'b']
t is ['a', 'b', 'c']
t is ['a', 'c', 'a']
t is ['a', 'c', 'b']
t is ['a', 'c', 'c']
t is ['b', 'a', 'a']
t is ['b', 'a', 'b']
t is ['b', 'a', 'c']
t is ['b', 'b', 'a']
t is ['b', 'b', 'b']
t is ['b', 'b', 'c']
t is ['b', 'c', 'a']
t is ['b', 'c', 'b']
t is ['b', 'c', 'c']
t is ['c', 'a', 'a']
t is ['c', 'a', 'b']
t is ['c', 'a', 'c']
t is ['c', 'b', 'a']
t is ['c', 'b', 'b']
t is ['c', 'b', 'c']
t is ['c', 'c', 'a']
t is ['c', 'c', 'b']
t is ['c', 'c', 'c']
t is ['a', 'a', 'a']
t is ['a', 'a', 'b']
t is ['a', 'a', 'c']
t is ['a', 'b', 'a']
t is ['a', 'b', 'b']
t is ['a', 'b', 'c']
t is ['a', 'c', 'a']
t is ['a', 'c', 'b']
t is ['a', 'c', 'c']
t is ['b', 'a', 'a']
t is ['b', 'a', 'b']
t is ['b', 'a', 'c']
t is ['b', 'b', 'a']
t is ['b', 'b', 'b']
t is ['b', 'b', 'c']
t is ['b', 'c', 'a']
t is ['b', 'c', 'b']
t is ['b', 'c', 'c']

下一步可以做的：写一个函数，输出字符串中字符的所有排序。（比如：abc acb bac bca cab cba）