def preserve(self, object, sexp):
        """
        (internal) Mark an object's persistent list for later referral.
        """
        # if I've been cooked in the meanwhile,
        if id(object) in self.cooked:
            # replace the placeholder empty list with the real one
            self.preserved[id(object)][2] = sexp
            # but give this one back.
            sexp = self.preserved[id(object)]
        else:
            self.preserved[id(object)] = sexp
        return sexp

        (internal) Mark an object's persistent list for later referral.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/spread/jelly.py