docs: def hkeys(self, name, key_start, key_end, limit=10):
          """
          Return a list of the top ``limit`` keys between ``key_start`` and
          ``key_end`` in hash ``name``
  
          Similiar with **Redis.HKEYS**        
  
          .. note:: The range is (``key_start``, ``key_end``]. The ``key_start``
             isn't in the range, but ``key_end`` is.
  
          :param string name: the hash name
          :param string key_start: The lower bound(not included) of keys to be
           returned, empty string ``''`` means -inf
          :param string key_end: The upper bound(included) of keys to be
           returned, empty string ``''`` means +inf
          :param int limit: number of elements will be returned.
          :return: a list of keys
          :rtype: list
          
          >>> ssdb.hkeys('hash_1', 'a', 'g', 10)
          ['b', 'c', 'd', 'e', 'f', 'g']
          >>> ssdb.hkeys('hash_2', 'key ', 'key4', 3)
          ['key1', 'key2', 'key3']
          >>> ssdb.hkeys('hash_1', 'f', '', 10)
          ['g']
          >>> ssdb.hkeys('hash_2', 'keys', '', 10)
          []
          """        
          limit = get_positive_integer('limit', limit)
          return self.execute_command('hkeys', name, key_start, key_end, limit)