I’ve been working with the Tornado web server pretty much since its release by the Facebook people several months ago. If you’ve never heard of it, it’s a sort of hybrid Python web framework and web server. On the framework side of the equation, Tornado has almost nothing. It’s completely bare bones when compared to something like Django. On the web server side, it is also pretty bare bones in terms of hardcore features like Apache’s ability to be a proxy and set up virtual hosts and all of that stuff. It does have some good performance numbers though, and the feature that seems to drive people to Tornado seems to be that it’s asynchronous, and pretty fast.
I think some people come away from their initial experiences with Tornado a little disheartened because only upon trying to benchmark their first real app do they come face to face with the reality of “asynchronous”: Tornado can be the best async framework out there, but the minute you need to talk to a resource for which there is no async driver, guess what? No async.
Some people might even leave the ring at this point, and that’s a shame, because to me the async features in Tornado aren’t what attract me to it at all.
Why Tornado, if Not For Async?
For me, there’s an enormous win in going with Tornado (or other things like it), and to get this benefit I’m willing to deal with some of Tornado’s warts and quirks. I’m willing to deal with the fact that the framework provides almost nothing I’m used to having after being completely spoiled by Django. What’s this magical feature you ask? It’s simply the knowledge that, in Tornado-land, there’s no such thing as mod_wsgi. And no mod_python either. There’s no mod_anything.
This means I don’t have to think about sys.path, relative vs. absolute paths, whether to use daemon or embedded mode, “Cannot be loaded as Python module” errors, “No such module” errors, permissions issues, subtle differences between Django’s dev server and Apache/mod_wsgi, reconciling all of these things when using/not using virtualenv, etc. It means I don’t have to metascript my way into a working application. I write the app. I run the app.
Wanna see how to create a Tornado app? Here’s one right here:
import tornado.httpserver import tornado.ioloop import tornado.web class MainHandler(tornado.web.RequestHandler): def get(self): self.write("This is a Tornado app") application = tornado.web.Application([ (r"/", MainHandler), ]) if __name__ == "__main__": http_server = tornado.httpserver.HTTPServer(application) http_server.listen(8888) tornado.ioloop.IOLoop.instance().start()
Save this to whatever file you want, run it, and do ‘curl http://localhost:8888′ and you’ll see ‘This is a Tornado app’ on your console.
Simplistic? Yes, absolutely. But when you can just run this script, put it behind nginx, and have it working in under five minutes, you dig a little deeper and see what else you can do with this thing. Turns out, you can do quite a bit.
Can I Do Real Work With This?
I’ve actually been involved in a production launch of a non-trivial service running on Tornado, and it was mind-numbingly easy. It was several thousand lines of Python, all of which was written by two people, and the prototype was up and running inside of a month. Moving from prototype to production was a breeze, and the site has been solid since its launch a few months ago.
Do You Miss Django?
I miss *lots* of things about Django, sure. Most of all I miss Django’s documentation, but Tornado is *so* small that you actually can find what you need in the source code in 2 minutes or less, and since there aren’t a ton of moving parts, when you find what you’re looking for, you just read a few lines and you’re done: you’re not going to be backtracking across a bunch of files to figure out the process flow.
I also miss a lot of what I call Django’s ‘magic’. It sure does a lot to abstract away a lot of work. In place of that work, though, you’re forced to take on a learning curve that is steeper than most. I think it’s worth getting to know Django if you’re a web developer who hasn’t seen it before, because you’ll learn a lot about Python and how to architect a framework by digging in and getting your hands dirty. I’ve read seemingly most books about Django, and have done some development work in Django as well. I love it, but not for the ease of deployment.
I spent more time learning how to do really simple things with Django than it took to:
- Discover Tornado
- Download/install and run ‘hello world’
- Get a non-trivial, commercial application production-ready and launch it.
Will You Still Work With (Django/Mingus/Pinax/Coltrane/Satchmo/etc)?
Sure. I’d rather not host it, but if I have to I’ll get by. These applications are all important, and I do like developing with them. It’s mainly deployment that I have issues with.
That’s not to say I wouldn’t like to see a more mature framework made available for Tornado either. I’ve worked on one, though it’s not really beyond the “app template” phase at this point. Once the app template is able to get out of its own way, I think more features will start to be added more quickly… but I digress.
In the end, the astute reader will note that my issue isn’t so much with Django-like frameworks (though I’ll note that they don’t suit every purpose), but rather with the current trend of using mod_wsgi for deployment. I’ll stop short of bashing mod_wsgi, because it too is an important project that has done wonders for the state of Python in web development. It really does *not* fit my brain at all, though, and I find when I step into a project that’s using it and it has mod_wsgi-related problems, identifying and fixing those problems is typically not a simple and straightforward affair.
So, if you’re like me and really want to develop on the web with Python, but mod_wsgi eludes you or just doesn’t fit your brain, I can recommend Tornado. It’s not perfect, and it doesn’t provide the breadth of features that Django does, but you can probably get most of your work done with it in the time it took you to get a mod_wsgi “Hello World!” app to not return a 500 error.