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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def launch(self, port=None):
 """ Run the app. """

        
        if port is not None:
            self.port = port
        url = 'http://127.0.0.1:{PORT}'.format(PORT=self.port)
        print('Interface starting at {url}'.format(url=url))
        self.listen(self.port)
        # webbrowser.open(url)
        tornado.ioloop.IOLoop.instance().start()