Tornado Server-Sent Event handler

gistfile1.py

class SSEHandler(tornado.web.RequestHandler):
    def initialize(self):
        self.set_header('Content-Type', 'text/event-stream')
        self.set_header('Cache-Control', 'no-cache')
            
    def emit(self, data, event=None):
        """
        Actually emits the data to the waiting JS
        """
        response = u''
        encoded_data = json.dumps(data)
        if event != None:
            response += u'event: ' + unicode(event).strip() + u'\n'
                
        response += u'data: ' + encoded_data.strip() + u'\n\n'

        self.write(response)
        self.flush()

You can just inherit like so:

class EventHandler(SSEHandler):
    def get(self):
        self.emit("hello")

If someone is looking for more help at making Server Side Events work, I found these two pages were useful:

https://gist.github.com/mivade/d474e0540036d873047f

https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format

(I link directly to the Event Stream Format section of the above page because that's particularly important. If you don't follow it, it won't work.)