Descriptor-based class function registry

registry.py

class FunctionNotFoundError(KeyError):
    pass

class Registry:
    def __init__(self):
        self.registry = {}

    def register(self, key):
        def decorator(func):
            self.registry[key] = func
            return func
        return decorator
    
    def lookup(self, key):
        try:
            return self.registry[key]
        except KeyError as e:
            raise FunctionNotFoundError(key) from e
    
    def make_bound(self, instance):
        def bound(*args, **kwargs):
            key, *args = args
            return self.lookup(key)(instance, *args, **kwargs)
        return bound

    def __get__(self, instance, owner):
        if instance is None:
            return self
        else:
            return self.make_bound(instance)


# Example
class EventHandler:
    registry = Registry()
    
    @registry.register('event1')
    def handle_event1(self, stuff):
        print('event1', stuff)
    
    @registry.register('event2')
    def handle_event2(self, stuff):
        print('event2', stuff)
    
    def handle_event(self, event_type, stuff):
        # Invoke the registry with self.registry and call it to do a lookup
        return self.registry(event_type, stuff)

handler = EventHandler()

handler.handle_event('event1', 'hello')
handler.handle_event('event2', 'world')