code: def __yield_handlers(self, event_type):
          
          if event_type not in self.event_types:
              raise ValueError("%r not found in %r.event_types == %r" % (event_type, self, self.event_types))
  
          # Search handler stack for matching event handlers
          for frame in list(self._event_stack):
              if event_type in frame:
                  yield frame[event_type]
  
          # Check instance for an event handler
          if hasattr(self, event_type):
              yield getattr(self, event_type)
docs: Yield all the handlers registered for the given event type.