Djangocon: Effortless real time apps in Django - Aaron Bassett¶

Tags: django, djangocon

(One of the summaries of a talk at the 2015 Djangocon EU conference).

Aaron Bassett says there are two kinds of polling you can do upon http: lots of small requests all the time, hoping that there’s something new on the server. And “long polling”, where a connection is opened and kept open until the server has something to send back. Once received, a new http request is send out.

But… in the core, that’s a hack. http isn’t designed for that.

Now there’s websockets. Persistent connections where you can send messages back and forth between server and browser.

There is a django package to make real time web easy: swamp dragon. Swamp dragon consists of:

• Redis. Basically a very quick, persistent kind of memcache. Supports pubsub.

• Tornado. A python webserver. Non-blocking IO. Lots of connections are no problem.

• Django.

Swamp dragon takes care of all the real time stuff for you. He made a sample TODO django app. Some notes:

• There’s a swamp dragon model mixin that makes sure any changes to the models are send to Redis.

• You have swamp dragon serializers that tell which data you want to extract from the models. And you can add extra information, of course.

  The serializers look a lot like django rest framework’s serializers. They’re working to support the DRF serializers. This helps with the code duplication you might have to have.

• The URLs are handled via ModelRouters.

• They used angularjs to talk to the websocket and keep the list of TODOs up to date.

He showed a demo. It looked to work really fast and responsive.

If you already have a django site, perhaps you’re not really interested in adding redis and so to the mix. You could look at software-as-a-service providers like firebase or pubnub or pusher (a conference sponsor).

They now use pusher. It has a python library to talk to it. So they replaced redis + tornado with pusher. Pusher also has an angularjs library, so that helped getting it running quickly.

His demo code is at https://github.com/aaronbassett/djangocon-pusher

He afterwards showed the third example to get notifications in django if someone else is editing the same object, including javascript integration: https://pypi.python.org/pypi/django-pusherable