Tornado Web Server

Tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed. By using non-blocking network I/O, Tornado can scale to tens of thousands of open connections, making it ideal for long polling, WebSockets, and other applications that require a long-lived connection to each user.

Upgrade notes

As of Tornado 3.2, the backports.ssl_match_hostname package must be installed when running Tornado on Python 2. This will be installed automatically when using pip or easy_install.

Quick links

• Documentation
• Source (github)
• Mailing list
• Stack Overflow
• Wiki

Hello, world

Here is a simple "Hello, world" example web 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()

This example does not use any of Tornado's asynchronous features; for that see this simple chat room.

Installation

Automatic installation:

pip install tornado

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 the latest source from PyPI.

::: parsed-literal tar xvzf tornado-$VERSION.tar.gz cd tornado-$VERSION python setup.py build sudo python setup.py install :::

The Tornado source code is hosted on GitHub.

Prerequisites: Tornado runs on Python 2.6, 2.7, 3.2, 3.3, and 3.4. It requires the certifi package on all Python versions, and the backports.ssl_match_hostname package on Python 2. These will be installed automatically when using pip or easy_install). Some Tornado features may require one of the following optional libraries:

• unittest2 is needed to run Tornado's test suite on Python 2.6 (it is unnecessary on more recent versions of Python)
• concurrent.futures is the recommended thread pool for use with Tornado and enables the use of tornado.netutil.ThreadedResolver. It is needed only on Python 2; Python 3 includes this package in the standard library.
• pycurl is used by the optional tornado.curl_httpclient. Libcurl version 7.18.2 or higher is required; version 7.21.1 or higher is recommended.
• Twisted may be used with the classes in [tornado.platform.twisted]{.title-ref}.
• pycares is an alternative non-blocking DNS resolver that can be used when threads are not appropriate.
• Monotime adds support for a monotonic clock, which improves reliability in environments where clock adjustments are frequent. No longer needed in Python 3.3.

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