python events

gistfile1.py

class Event(object):
    def __init__(self):
        self._callbacks = set()

    def fire(self, *args, **kwargs):
        for callback in self._callbacks:
            try:
                callback(*args, **kwargs)
            except Exception:
                LOG.exception('Error during event callback')

    def __iadd__(self, callback):
        if not callable(callback):
            raise ValueError('Invalid callback registered')
        self._callbacks.add(callback)
        return self

    def __isub__(self, callback):
        self._callbacks.remove(callback)
        return self


def message_handler(message):
    print message

on_message = Event()
on_message += message_handler

on_message.fire('hello world')