Python 3: registry with auto-subclass registration

subclass_registry.py

from abc import abstractmethod
from collections import defaultdict
from dataclasses import dataclass
from typing import Any
from typing import Union


@dataclass(frozen=True)
class Event:
    name: str
    payload: Any


class EventHandler:
    # This is a class attr
    _event_registry = defaultdict(list)

    def __init__(self, event):
        self._handle(event)  # required to be implemented by subclasses

    @staticmethod
    @abstractmethod
    def _handle(event) -> Any:
        raise NotImplementedError

    def __init_subclass__(cls):
        """Automatic subclass registration.

        This method is called whenever the containing class is subclassed.
        """
        if not hasattr(cls, "event_type"):
            raise TypeError("Subclasses must define an event_type")
        cls._event_registry[cls.event_type].append(cls)

    @classmethod
    def registered_handlers(cls, event: Union[Event, str]):
        if isinstance(event, Event):
            event = event.name
        return cls._event_registry[event]


class FlightHandlerOne(EventHandler):
    event_type = "flight"

    @staticmethod
    def _handle(event: Event):
        print(event.payload)


class FlightHandlerTwo(EventHandler):
    event_type = "flight"

    @staticmethod
    def _handle(event: Event):
        for ch in list(event.payload):
            print(ch)


for handler in EventHandler.registered_handlers("flight"):
    some_event = Event("flight", "some payload")
    handler(some_event)
    
'''
$ python subclass_registry.py
some payload
s
o
m
e

p
a
y
l
o
a
d
'''