docs: def zavg(self, name, score_start, score_end):
          """
          Returns the average of elements of the sorted set stored at the
          specified key which have scores in the range [score_start,score_end].        
          
          .. note:: The range is [``score_start``, ``score_end``]
  
          :param string name: the zset name
          :param int score_start: The minimum score related to keys(included),
           empty string ``''`` means -inf
          :param int score_end: The maximum score(included) related to keys,
           empty string ``''`` means +inf
          :return: the average of keys in specified range
          :rtype: int
          
          >>> ssdb.zavg('zset_1', 20, 70)
          38
          >>> ssdb.zavg('zset_1', 0, 100)
          35
          >>> ssdb.zavg('zset_1', 2, 3)
          0
          """        
          score_start = get_integer_or_emptystring('score_start', score_start)
          score_end = get_integer_or_emptystring('score_end', score_end)
          return self.execute_command('zavg', name, score_start, score_end)