@classmethod
def _get_backend_type(cls, value):
    """
        helper to resolve backend constant from type
        """
    try:
        return cls._backend_type_map[value]
    except KeyError:
        pass
    msg = 'unsupported argon2 hash (type %r not supported by %s backend)' % (
        value, cls.get_backend())
    raise ValueError(msg)
