chain pattern | Python Fiddle

class Event:
	def __init__(self, name):
		self.name = name

def __str__(self):
		return self.name

class Widget:
	def __init__(self, parent=None):
		self.parent = parent

def handle(self, event):
		handler = 'handle_{}'.format(event)
		if hasattr(self, handler):
			method = getattr(self, handler)
			method(event)
		elif self.parent:
			self.parent.handle(event)
		elif hasattr(self, 'handle_default'):
			self.handle_default(event)

class MainWindow(Widget):
	def handle_close(self, event):
		print('MainWindow: {}'.format(event))

def handle_default(self, event):
		print('MainWindow Default: {}'.format(event))

class SendDialog(Widget):
	def handle_paint(self, event):
		print('SendDialog: {}'.format(event))

class MsgText(Widget):
	def handle_down(self, event):
		print('MsgText: {}'.format(event))

def main():
	mw = MainWindow()
	sd = SendDialog(mw)
	msg = MsgText(sd)

for e in ('down', 'paint', 'unhandled', 'close'):
		evt = Event(e)
		print('\nSending event -{}- to MainWindow'.format(evt))
		mw.handle(evt)
		print('Sending event -{}- to SendDialog'.format(evt))
		sd.handle(evt)
		print('Sending event -{}- to MsgText'.format(evt))
		msg.handle(evt)

if __name__ == '__main__':
    main()

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