def _ancillaryDescriptor(fd):
    """
    Pack an integer into an ancillary data structure suitable for use with
    L{sendmsg.sendmsg}.
    """
    packed = struct.pack("i", fd)
    return [(socket.SOL_SOCKET, sendmsg.SCM_RIGHTS, packed)]

    Pack an integer into an ancillary data structure suitable for use with
    L{sendmsg.sendmsg}.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/unix.py