def jellyFor(self, jellier):
        """
        If I am being sent back to where I came from, serialize as a local backreference.
        """
        if jellier.invoker:
            assert self.broker == jellier.invoker, "Can't send references to brokers other than their own."
            return b"local", self.luid
        else:
            return b"unpersistable", "References cannot be serialized"

        If I am being sent back to where I came from, serialize as a local backreference.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/spread/pb.py