def _killBackref( receiver, senderkey ):
    """Do the actual removal of back reference from receiver to senderkey"""
    receiverkey = id(receiver)
    set = sendersBack.get( receiverkey, () )
    while senderkey in set:
        try:
            set.remove( senderkey )
        except:
            break
    if not set:
        try:
            del sendersBack[ receiverkey ]
        except KeyError:
            pass
    return True
Do the actual removal of back reference from receiver to senderkey