class AdvancedIterator def __init__ self sequence self sequence sequen

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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