code: def _has_expired(self):
          
          expired = False
          if hasattr(self, 'Expiration'):
              now = datetime.datetime.utcnow()
              expiration = datetime.datetime.strptime(self.Expiration, '%Y-%m-%dT%H:%M:%SZ')
              expired = (now >= expiration)
          else:
              raise ValueError("ERROR: Request for expired property, but no Expiration in HIT!")
          return expired
docs: Has this HIT expired yet?