Event Dispatcher Example

This example demonstrates using dictionary dispatching to implement event handlers. Rather than a block of conditional logic (if/else statements), I use a dictionary to register, lookup, and invoke event handlers (functions) given a key. This pattern is used by popular Python libraries like Flask and FastAPI to dispatch requests. It is also used by the functools.singledispatch() decorator to implement function overloading based on the type of the function's first argument.

This example is a simplified version of an event dispatacher I built to register event handlers for events arriving from Kafka in an event-driven architecture. Metadata in each Kafka message (event) includes a key to identify the event type which is then used to dispatch the event to the appropriate handler.

• dispatcher.py defines the @event_dispatcher decorator. The registry function member is the dictionary from which handlers are registered and invoked. The Message dataclass is also defined here for simplicity.
• handlers.py defines the event handler functions for the events that we intend to handle as well as a default handler.
• examples.py provides an example of using this event dispatcher. It creates some example messages and then calls the handlers.handle_event() function to lookup the event handler based on the event type in the Message.