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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def keys(self, name_start, name_end, limit=10):
 """ Return a list of the top ``limit`` keys between ``name_start`` and ``name_end`` Similiar with **Redis.KEYS** .. note:: The range is (``name_start``, ``name_end``]. ``name_start`` isn't in the range, but ``name_end`` is. :param string name_start: The lower bound(not included) of keys to be returned, empty string ``''`` means -inf :param string name_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 ['set_x2', 'set_x3'] ['set_x1', 'set_x2', 'set_x3'] ['set_x1', 'set_x2', 'set_x3', 'set_x4'] [] """

        limit = get_positive_integer('limit', limit)
        return self.execute_command('keys', name_start, name_end, limit)