I don't understand this recursive method in python to generate permutations -

how recursive method work generate permutations given string? explain me please?

def exchange(self, s):     if 0 == len(s):         yield s     else:         in range(len(s)):             p in self.exchange(s[:i] + s[i + 1:]):                 yield [s[i]] + p 

the code has following idea: deliver permutations choosing 1 element input , deliver permutations of remaining elements, prepended chosen element. after this, repeat element.

so, if have input [0, 1, 2], code uses first element (0) , builds permutations of remaining elements (1 , 2). (these permutations [1, 2] , [2, 1] of course.)

then delivers (yields) 0 prepended [1, 2] , 0 prepended [2, 1], i. e. [0, 1, 2] , [0, 2, 1].

then continues , chooses next element (1). builds permutations of remaining elements (0, 2) (i. e. [0, 2] , [2, 0]).

and forth.