def add_converter(cls, klass, conv, score=0):
        """ Add converter
        :param klass: class or str
        :param conv: callable
        :param score:
        :return:
        """
        if isinstance(klass, str):
            klass = import_name(klass)
        item = klass, conv, score
        cls.converters.append(item)
        cls.converters.sort(key=lambda x: x[0])
        return cls