P_iter should have an __iter__ method to fully comply with the iterator protocol:

 def __iter__(self):
     return self

Defining the P_iter class inside a method hurts readability and makes the class unavailable for anyone who wants to check the type of an iterator object.

P_iter should have an __iter__ method to fully comply with the iterator protocol:

 def __iter__(self):
     return self

Defining the P_iter class inside a method hurts readability and makes the class unavailable for anyone who wants to check the type of an iterator object.

In Permutation2.__iter__ I would use this approach to avoid the stahp variable :

 def __iter__(self):
     curr = self.start
     while True:
         yield curr
         curr = self.p[curr]
         if curr == self.start:
             return