Can't use the same listener with different filters

[corranwebster]

In the events API you can't bind the same function callback to the same class with different filters. The actual behaviour is somewhat surprising:

from encore.events.api import EventManager, BaseEvent
em = EventManager()

def listener(event):
    print event.source

em.connect(BaseEvent, listener, filter={'source': 1})
em.emit(BaseEvent(source=1)) # prints 1
em.emit(BaseEvent(source=2)) # doesn't fire
em.connect(BaseEvent, listener, filter={'source': 2})
em.emit(BaseEvent(source=1)) # doesn't fire
em.emit(BaseEvent(source=2)) # fires twice, printing 2 each time

I think it is reasonable to have the same callback bound with two different filters; however even if it isn't then binding the same function with a different filter should probably remove the old function.

[pankajp]

Thanks for catching the bug. What do u believe should happen, disconnect old or add another. My thinking was the latter, since otherwise disconnecting may also need filter specification.

[corranwebster]

It would be nice if we could use the same callback with different filters,
but it's not absolutely essential, since you can work around by creating
instances of callable classes.

The pros of having a single callback work with multiple filters is that
this sort of pattern is fairly natural:

for obj in object_list:
    if obj.some_condition():
        event_manager.connect(MyEvent, my_callback, filter={'source':

obj})

You can't do this if you replace the filter.

The cons of having a single callback work with multiple filters are that
you now have to specify the filter as well as the event class and function.

One possible alternative approach: have the filter specified as an
attribute on the callable, which makes it clearer that you need to have
separate objects for each filter). You could do this for functions via:

def my_callback(evt):
    ...
my_callback.filter = {...}

I'm not sure what's the best approach myself.

On Wed, Jan 4, 2012 at 9:01 AM, Pankaj Pandey <
reply@reply.github.com

wrote:

Thanks for catching the bug. What do u believe should happen, disconnect
old or add another. My thinking was the latter, since otherwise
disconnecting may also need filter specification.

---

Reply to this email directly or view it on GitHub:
#2 (comment)