def resolve_ptr(tor_endpoint, ip):
    """
    This is easier to use via :meth:`txtorcon.Tor.dns_resolve_ptr`

    :param tor_endpoint: the Tor SOCKS endpoint to use.

    :param ip: the IP address to look up.
    """
    if six.PY2 and isinstance(ip, str):
        ip = unicode(ip)  # noqa
    elif six.PY3 and isinstance(ip, bytes):
        ip = ip.decode('ascii')
    factory = _TorSocksFactory(
        ip, 0, 'RESOLVE_PTR', None,
    )
    proto = yield tor_endpoint.connect(factory)
    result = yield proto.when_done()
    returnValue(result)