events.rst

Using Object Events in Pyramid

Warning

This code works only in Pyramid 1.1a4+. It will also make your brain explode.

Zope's Component Architecture supports the concept of "object events", which are events which call a subscriber with an context object and the event object.

Here's an example of using an object event subscriber via the @subscriber decorator:

 from zope.component.event import objectEventNotify
 from zope.component.interfaces import ObjectEvent

 from pyramid.events import subscriber
 from pyramid.view import view_config

 class ObjectThrownEvent(ObjectEvent):
     pass

 class Foo(object):
   pass

 @subscriber([Foo, ObjectThrownEvent])
 def objectevent_listener(object, event):
     print object, event

 @view_config(renderer='string')
 def theview(request):
     objectEventNotify(ObjectThrownEvent(Foo()))
     objectEventNotify(ObjectThrownEvent(None))
     objectEventNotify(ObjectEvent(Foo()))
     return 'OK'

 if __name__ == '__main__':
     from pyramid.config import Configurator
     from paste.httpserver import serve
     config = Configurator(autocommit=True)
     config.hook_zca()
     config.scan('__main__')
     serve(config.make_wsgi_app())

The objectevent_listener listener defined above will only be called when the object of the ObjectThrownEvent is of class Foo. We can tell that's the case because only the first call to objectEventNotify actually invokes the subscriber. The second and third calls to objectEventNotify do not call the subscriber. The second call doesn't invoke the subscriber because its object type is None (and not Foo). The third call doesn't invoke the subscriber because its objectevent type is ObjectEvent (and not ObjectThrownEvent). Clear as mud?