How to run functions outside websocket loop in python (tornado)

Question

I'm trying to set up a small example of a public Twitter stream over websockets. This is my websocket.py, and it's working.

What I'm wondering is: how can I interact with the websocket from 'outside' the class WSHandler (ie. not only answer when receiving a message from websocket.js)? Say I want to run some other function within this same script that would post "hello!" every five seconds and send that to the websocket (browser) without any interaction from client-side. How could I do that?

So it's kind of a fundamental beginner's question, I suppose, about how to deal with classes as those below. Any pointers in any direction would be greatly appreciated!

import os.path
import tornado.httpserver
import tornado.websocket
import tornado.ioloop
import tornado.web

# websocket
class FaviconHandler(tornado.web.RequestHandler):
    def get(self):
        self.redirect('/static/favicon.ico')

class WebHandler(tornado.web.RequestHandler):
    def get(self):
        self.render("websockets.html")

class WSHandler(tornado.websocket.WebSocketHandler):
    def open(self):
        print 'new connection'
        self.write_message("Hi, client: connection is made ...")

    def on_message(self, message):
        print 'message received: \"%s\"' % message
        self.write_message("Echo: \"" + message + "\"")
        if (message == "green"):
            self.write_message("green!")

    def on_close(self):
        print 'connection closed'



handlers = [
    (r"/favicon.ico", FaviconHandler),
    (r'/static/(.*)', tornado.web.StaticFileHandler, {'path': 'static'}),
    (r'/', WebHandler),
    (r'/ws', WSHandler),
]

settings = dict(
    template_path=os.path.join(os.path.dirname(__file__), "static"),
)

application = tornado.web.Application(handlers, **settings)

if __name__ == "__main__":
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(8888)
    tornado.ioloop.IOLoop.instance().start()

Answer 1

You could call a

IOLoop.add_timeout(deadline, callback)

that calls the callback at specified deadline timeout (one shot, but you can reschedule), or use the

tornado.ioloop.PeriodicCallback if you have a more periodic task.

See: http://www.tornadoweb.org/en/stable/ioloop.html#tornado.ioloop.IOLoop.add_timeout

Update: some example

import datetime

def test():
    print "scheduled event fired"
...

if __name__ == "__main__":
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(8888)
    main_loop = tornado.ioloop.IOLoop.instance()
    # Schedule event (5 seconds from now)
    main_loop.add_timeout(datetime.timedelta(seconds=5), test)
    # Start main loop
    main_loop.start()

it calls test() after 5 seconds.

Update 2:

import os.path
import tornado.httpserver
import tornado.websocket
import tornado.ioloop
import tornado.web

# websocket
class FaviconHandler(tornado.web.RequestHandler):
    def get(self):
        self.redirect('/static/favicon.ico')

class WebHandler(tornado.web.RequestHandler):
    def get(self):
        self.render("websockets.html")

class WSHandler(tornado.websocket.WebSocketHandler):
    def open(self):
        print 'new connection'
        self.write_message("Hi, client: connection is made ...")
        tornado.ioloop.IOLoop.instance().add_timeout(datetime.timedelta(seconds=5), self.test)

    def on_message(self, message):
        print 'message received: \"%s\"' % message
        self.write_message("Echo: \"" + message + "\"")
        if (message == "green"):
            self.write_message("green!")

    def on_close(self):
        print 'connection closed'

    def test(self):
        self.write_message("scheduled!")

handlers = [
    (r"/favicon.ico", FaviconHandler),
    (r'/static/(.*)', tornado.web.StaticFileHandler, {'path': 'static'}),
    (r'/', WebHandler),
    (r'/ws', WSHandler),
]

settings = dict(
    template_path=os.path.join(os.path.dirname(__file__), "static"),
)

application = tornado.web.Application(handlers, **settings)

import datetime

if __name__ == "__main__":
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(8888)
    tornado.ioloop.IOLoop.instance().start()