code: def count(self, start, stop):
          '''Count the number of elements bewteen *start* and *stop*.'''
          s1 = self.pickler.dumps(start)
          s2 = self.pickler.dumps(stop)
          return self.backend_structure().count(s1, s2f count(self, start, stop):
          '''Count the number of elements bewteen *start* and *stop*.'''
          s1 = self.pickler.dumps(start)
          s2 = self.pickler.dumps(stop)
          return self.backend_structure().count(s1, s2)
docs: Count the number of elements bewteen *start* and *stop*.