Invoke an application event handler.

def _trigger_event(self, event, namespace, *args):
        """Invoke an application event handler."""
        # first see if we have an explicit handler for the event
        if namespace in self.handlers and event in self.handlers[namespace]:
            return self.handlers[namespace][event](*args)

        # or else, forward the event to a namespace handler if one exists
        elif namespace in self.namespace_handlers:
            return self.namespace_handlers[namespace].trigger_event(
                event, *args)