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)
        []

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)