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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_obsolete(self):
 """returns True is data is obsolete and needs revalidation """

        if self.cache_updated:
            now = timezone.now()
            delta = now - self.cache_updated
            if delta.seconds < self.cache_validity:
                return False
        return True