def insert(self, event_key, propagate):
        target = event_key.dispatch_target
        assert isinstance(target, type), \
            "Class-level Event targets must be classes."
        stack = [target]
        while stack:
            cls = stack.pop(0)
            stack.extend(cls.__subclasses__())
            if cls is not target and cls is self._clslevel:
                self.update_subclass(cls)
            else:
                if cls not in self._clslevel:
                    self._clslevel[cls] = collections.deque()
                self._clslevel[cls].appendleft(event_key._listen_fn)
        registry._stored_in_collection(event_key, self)
dataset/ETHPy150Open zzzeek/sqlalchemy/lib/sqlalchemy/event/attr.py/_ClsLevelDispatch.insert/operator `not in` -> `is`