Is this possible with decorators?

Question

I'm new to python and I'm exploring my way through the language while building real applications. Right now I'm trying to build an event-based app, and was thinking about using decorators as a way to add functions as listeners:

@onEvent(eventSpecificArgument)
def foo():
    print('foo')

In the above example, I have added the function foo as a listener for the event, and have passed an argument that will be used by the decorator.

Is this a possible (and smart enough) solution for what I want? And if it is, how could/should I implement it?

Answer 1

Sure, decorators are just callables. Decorator notation is just syntactic sugar, your example translates to:

def foo():
    print('foo')
foo = onEvent(eventSpecificArgument)(foo)

so your onEvent() callable needs to return something that can be called; that 'something' will be passed in foo.

Whatever you do in onEvent and in the 'something' it returned is up to you.

Something like the following would work:

registry = {}

def onEvent(eventname):
    def eventdecorator(func):
        registry.setdefault(eventname, []).append(func)
        return func
    return eventdecorator

This just adds func to the registry for a given eventname and returns the function unchanged.

Later on, when you then need to handle the event, you just look up the event handlers for that event with:

for func in registry.get(eventname, ()):
    func()