Return a TimeMachine for the object on which this action was 
        performed and at the time of this action.

def __get_timemachine(self):
        """Return a TimeMachine for the object on which this action was 
        performed and at the time of this action."""
        if not self.__timemachine:
            self.__timemachine = TimeMachine(
                self.object_uid,
                step = self.id,
            )

        return self.__timemachine.at(self.id)