Python Tornado webserver that streams JPEGs (in img/) as MJPEG-Stream using asynchronous timed callbacks (yields), being able to handly many different streams at the same time

Tornado webserver MJPEG streamer

import tornado.ioloop
import tornado.web
import gen
import time
import os
import tornado

file_list = os.listdir("img")
counter = 0


def current_jpeg():
    img = None
    global counter
    with open("img/" + file_list[counter]) as f:
       img = f.read()
    counter = (counter + 1) % len(file_list)
    return  img


class MJPEGHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    @tornado.gen.coroutine
    def get(self):
        ioloop = tornado.ioloop.IOLoop.current()

        self.set_header('Cache-Control', 'no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0')
        self.set_header('Connection', 'close')
        self.set_header( 'Content-Type', 'multipart/x-mixed-replace;boundary=--boundarydonotcross')
        self.set_header('Expires', 'Mon, 3 Jan 2000 12:34:56 GMT')
        self.set_header( 'Pragma', 'no-cache')


        self.served_image_timestamp = time.time()
        my_boundary = "--boundarydonotcross\n"
        while True:
            img = current_jpeg()
            interval = 1.0
            if self.served_image_timestamp + interval < time.time():
                self.write(my_boundary)
                self.write("Content-type: image/jpeg\r\n")
                self.write("Content-length: %s\r\n\r\n" % len(img))
                self.write(str(img))
                self.served_image_timestamp = time.time()
                yield tornado.gen.Task(self.flush)
            else:
                yield tornado.gen.Task(ioloop.add_timeout, ioloop.time() + interval)


application = tornado.web.Application([
    (r"/", MJPEGHandler),
])


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