old_contents: import tornado.ioloop
  import tornado.web
  
  class MainHandler(tornado.web.RequestHandler):
      def get(self):
          self.write("Hello, world")
  
  application = tornado.web.Application([
      (r"/", MainHandler),
  ])
  
  if __name__ == "__main__":
      application.listen(8888)
      tornado.ioloop.IOLoop.instance().start()
  
new_contents: import tornado.ioloop
  import tornado.web
  
  
  class MainHandler(tornado.web.RequestHandler):
      def get(self):
          self.write("Hello, world")
  
  
  class EventHandler(tornado.web.RequestHandler):
      def post(self):
          print self.request.body
  
  
  application = tornado.web.Application([
      (r"/", MainHandler),
      (r"/event", EventHandler),
  ])
  
  if __name__ == "__main__":
      application.listen(19090)
      tornado.ioloop.IOLoop.instance().start()
  
subject: Add event listener