class AdvancedIterator: def __init__(self,sequence): self.sequence=sequence self.index=-1 def _next(self): try: return self.sequence[self.index+1] except IndexError: raise StopIteration def _previous(self): if self.index<0: raise StopIteration return self.sequence[self.index] def next(self): item=self._next() self.index+=1 return item def previuos(self): item=self._previous() self.index-=1 return item