tar xvzf tornado-4.3.tar.gz
cd tornado-4.3
python setup.py build
python setup.py install

import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")
def make_app():
    return tornado.web.Application([
        (r"/", MainHandler),
    ])
if __name__ == "__main__":
    app = make_app()
    app.listen(9000)
    tornado.ioloop.IOLoop.current().start()

python app.py

ERR_CONNECTION_TIMED_OUT

Traceback (most recent call last):
  File "app.py", line 29, in <module>
    tornado.ioloop.IOLoop.current().start()
  File "/root/tornado/tornado-4.3/tornado/ioloop.py", line 858, in start
    event_pairs = self._impl.poll(poll_timeout)
KeyboardInterrupt

import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web
from tornado.options import define, options
define("port", default=8686, help="run on the given port", type=int)
class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")
def main():
    tornado.options.parse_command_line()
    application = tornado.web.Application([
        (r"/", MainHandler),
    ])
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(options.port)
    tornado.ioloop.IOLoop.current().start()
if __name__ == "__main__":
    main()

Traceback (most recent call last):
  File "demos/helloworld/helloworld.py", line 43, in <module>
    main()
  File "demos/helloworld/helloworld.py", line 39, in main
    tornado.ioloop.IOLoop.current().start()
  File "/usr/lib64/python2.6/site-packages/tornado-4.3-py2.6-linux-x86_64.egg/tornado/ioloop.py", line 858, in start
    event_pairs = self._impl.poll(poll_timeout)
KeyboardInterrupt