def random_list_elem(str_list):
        """
        :param str_list: a pre-defined string list
        :return: SeedString()
        """
        if isinstance(str_list, list):
            for elem in str_list:
                if not isinstance(elem, str):
                    raise TypeError("list element can only be string")
            return SeedString(random.choice(str_list))
        return None