Tornado is an open source version of the scalable, non-blocking web server and tools that power FriendFeed. The FriendFeed application is written using a web framework that looks a bit like web.py or Google's webapp, but with additional tools and optimizations to take advantage of the underlying non-blocking infrastructure.

The framework is distinct from most mainstream web server frameworks (and certainly most Python frameworks) because it is non-blocking and reasonably fast. Because it is non-blocking and uses epoll or kqueue, it can handle thousands of simultaneous standing connections, which means it is ideal for real-time web services. We built the web server specifically to handle FriendFeed's real-time features — every active user of FriendFeed maintains an open connection to the FriendFeed servers. (For more information on scaling servers to support thousands of clients, see The C10K problem.)

Upgrading from Tornado 1.x

Tornado 2.0 introduces several potentially backwards-incompatible changes, including in particular automatic escaping of template output. Users who are upgrading from Tornado 1.x should see the release notes for information about backwards compatibility.

Quick links

• Documentation
• Download version 2.2 (release notes)
• Source (github)
• Mailing list
• Wiki

Hello, world

Here is the canonical "Hello, world" example app for Tornado:

import tornado.ioloop
import tornado.web

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")

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

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

See the Tornado documentation for a detailed walkthrough of the framework.

Installation

Automatic installation: Tornado is listed in PyPI and can be installed with pip or easy_install. Note that the source distribution includes demo applications that are not present when Tornado is installed in this way, so you may wish to download a copy of the source tarball as well.

Manual installation: Download tornado-2.2.tar.gz

tar xvzf tornado-2.2.tar.gz
cd tornado-2.2
python setup.py build
sudo python setup.py install

The Tornado source code is hosted on GitHub. On Python 2.6 and 2.7, it is also possible to simply add the tornado directory to your PYTHONPATH instead of building with setup.py, since the standard library includes epoll support.

Prerequisites: Tornado runs on Python 2.5, 2.6, 2.7 and 3.2.

• On Python 2.6 and 2.7, there are no dependencies outside the Python standard library, although PycURL (version 7.18.2 or higher required; version 7.21.1 or higher recommended) may be used if desired.
• On Python 2.5, PycURL is required, along with simplejson and the Python development headers (typically obtained by installing a package named something like python-dev from your operating system).
• On Python 3.2, the distribute package is required. Note that Python 3 support is relatively new and may have bugs.

Platforms: Tornado should run on any Unix-like platform, although for the best performance and scalability only Linux and BSD (including BSD derivatives like Mac OS X) are recommended.

Discussion and support

You can discuss Tornado and report bugs on the Tornado developer mailing list. Links to additional resources can be found on the Tornado wiki.