Class dispatcher

lib/sqlalchemy/event/base.py:428–460

Descriptor used by target classes to deliver the _Dispatch class at the class level and produce new _Dispatch instances for target instances.

class dispatcher(Generic[_ET]):
    """Descriptor used by target classes to
    deliver the _Dispatch class at the class level
    and produce new _Dispatch instances for target
    instances.

    """

    def __init__(self, events: Type[_HasEventsDispatch[_ET]]):
        self.dispatch = events.dispatch
        self.events = events

    @overload
    def __get__(
        self, obj: Literal[None], cls: Type[Any]
    ) -> Type[_Dispatch[_ET]]: ...

    @overload
    def __get__(self, obj: Any, cls: Type[Any]) -> _DispatchCommon[_ET]: ...

    def __get__(self, obj: Any, cls: Type[Any]) -> Any:
        if obj is None:
            return self.dispatch

        disp = self.dispatch._for_instance(obj)
        try:
            obj.__dict__["dispatch"] = disp
        except AttributeError as ae:
            raise TypeError(
                "target %r doesn't have __dict__, should it be "
                "defining _slots_dispatch?" % (obj,)
            ) from ae
        return disp


class slots_dispatcher(dispatcher[_ET]):