I really like that Tornado is a small, self-contained project. I can read through the whole codebase and understand it.

Twisted is quite large nowadays http://twistedmatrix.com/trac/browser/trunk/twisted

Compare it to Tornado source, which is ~30 Python files https://github.com/facebook/tornado/tree/master/tornado

I think that's because Tornado is fantastically simple, and Twisted just isn't.

Tornado is the bare-bones essentials for an async web application server. Twisted is not. You can start with Tornado, then put Django or Twisted on top, but that's optional.

Besides, people are kind of scared of Twisted.

I don't know if that many people inside the python community care either. Twisted is very big, documentation seriously lacking, and a lot of stuff in twisted not that useful if you only care about http. If you care about http, twisted is not that useful either (there is for example no http 1.1 support client-side AFAIK).

It would also have made porting tornado to python 3 a huge effort (given twisted code size).

when Tornado was first released, there was a lot of discussion online on various forums and comment threads about why it wasn't built on top of Twisted, or why it was a complete separate project.

I tend to agree with Brett Taylor in that Twisted was too large a project to suit the goals of Tornado, and that its own divisions within twisted.web were difficult to navigate through

the event handling part of Tornado is less than 100 lines of code and is a lot easier to implement and understand than Twisted, although Twisted also serves a purpose. I like and prefer that Tornado is self-contained and focuses on a single use case (returning JSON in long-polls) and does it well

I think it's safe to say a lot of people inside the Python community don't care either. Twisted is incredibly complex and competition in the asynchronous networking space can only be a good thing.

I stand on the other end. The reason why I choose tornado for my startup was because it did not use twisted (too early for twisted in my project). Tornado has a great modular structure so you can use each module on its own. The code is lovely to look at too.

> it's disappointing to see that Tornado still doesn't use Twisted

not using Twisted was the whole point of Tornado, wasn't it? If Tornado used Twisted it wouldn't exist.

Why would it switch to Twisted if it has always had its own lightweight event loop that's always benchmarked significantly faster? Same goes for fapws3 and gevent.

There are some philosophical reasons for not using twisted's io loop (for example, because it uses ctypes to interface with epoll et al, or because of the FactoryFactoryFactory Java envy).

As was mentioned already, competition is good.

You can have Tornado on Twisted, if you really want it: https://github.com/fiorix/cyclone

I have used this in a few applications and really liked it.

They've historically kept up with new Tornado releases, so hopefully they'll catch up with Tornado 2.0

What advantages would switching to Twisted bring to the Tornado project?

I'm glad to see that, out of all the top-level comments, the ones about Flask and Jinja2 were not highly criticized, but I will never understand the rather massive butthurt that this community seems to feel over Twisted. Is it because people love Tornado, or because people hate Twisted?

Also, as always, since somebody said "Twisted is big," I'd just like to counter: Django is twice as big as Twisted and nobody seems to mind.