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.

Quick links

• Current version: 4.5.3 (download from PyPI, release notes)
• Source (github)
• Mailing lists: discussion and announcements
• 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")

def make_app():
    return tornado.web.Application([
        (r"/", MainHandler),
    ])

if __name__ == "__main__":
    app = make_app()
    app.listen(8888)
    tornado.ioloop.IOLoop.current().start()

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

Installation

pip install tornado

Tornado is listed in PyPI and can be installed with pip. 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 or clone the git repository as well.

Prerequisites: Tornado runs on Python 2.7, and 3.3+ For Python 2, version 2.7.9 or newer is strongly recommended for the improved SSL support. In addition to the requirements which will be installed automatically by pip or setup.py install, the following optional packages may be useful:

• concurrent.futures is the recommended thread pool for use with Tornado and enables the use of 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 7.22 or higher is required.
• Twisted may be used with the classes in tornado.platform.twisted.
• pycares is an alternative non-blocking DNS resolver that can be used when threads are not appropriate.
• monotonic or Monotime add support for a monotonic clock, which improves reliability in environments where clock adjustements are frequent. No longer needed in Python 3.3.

Platforms: Tornado should run on any Unix-like platform, although for the best performance and scalability only Linux (with epoll) and BSD (with kqueue) are recommended for production deployment (even though Mac OS X is derived from BSD and supports kqueue, its networking performance is generally poor so it is recommended only for development use). Tornado will also run on Windows, although this configuration is not officially supported and is recommended only for development use. Without reworking Tornado IOLoop interface, it’s not possible to add a native Tornado Windows IOLoop implementation or leverage Windows’ IOCP support from frameworks like AsyncIO or Twisted.

Documentation

This documentation is also available in PDF and Epub formats.

• User’s guide
  • Introduction
  • Asynchronous and non-Blocking I/O
  • Coroutines
  • Queue example - a concurrent web spider
  • Structure of a Tornado web application
  • Templates and UI
  • Authentication and security
  • Running and deploying
• Web framework
  • tornado.web — RequestHandler and Application classes
  • tornado.template — Flexible output generation
  • tornado.routing — Basic routing implementation
  • tornado.escape — Escaping and string manipulation
  • tornado.locale — Internationalization support
  • tornado.websocket — Bidirectional communication to the browser
• HTTP servers and clients
  • tornado.httpserver — Non-blocking HTTP server
  • tornado.httpclient — Asynchronous HTTP client
  • tornado.httputil — Manipulate HTTP headers and URLs
  • tornado.http1connection – HTTP/1.x client/server implementation
• Asynchronous networking
  • tornado.ioloop — Main event loop
  • tornado.iostream — Convenient wrappers for non-blocking sockets
  • tornado.netutil — Miscellaneous network utilities
  • tornado.tcpclient — IOStream connection factory
  • tornado.tcpserver — Basic IOStream-based TCP server
• Coroutines and concurrency
  • tornado.gen — Simplify asynchronous code
  • tornado.concurrent — Work with threads and futures
  • tornado.locks – Synchronization primitives
  • tornado.queues – Queues for coroutines
  • tornado.process — Utilities for multiple processes
• Integration with other services
  • tornado.auth — Third-party login with OpenID and OAuth
  • tornado.wsgi — Interoperability with other Python frameworks and servers
  • tornado.platform.asyncio — Bridge between asyncio and Tornado
  • tornado.platform.caresresolver — Asynchronous DNS Resolver using C-Ares
  • tornado.platform.twisted — Bridges between Twisted and Tornado
• Utilities
  • tornado.autoreload — Automatically detect code changes in development
  • tornado.log — Logging support
  • tornado.options — Command-line parsing
  • tornado.stack_context — Exception handling across asynchronous callbacks
  • tornado.testing — Unit testing support for asynchronous code
  • tornado.util — General-purpose utilities
• Frequently Asked Questions
• Release notes
  • What’s new in Tornado 4.5.3
  • What’s new in Tornado 4.5.2
  • What’s new in Tornado 4.5.1
  • What’s new in Tornado 4.5
  • What’s new in Tornado 4.4.3
  • What’s new in Tornado 4.4.2
  • What’s new in Tornado 4.4.1
  • What’s new in Tornado 4.4
  • What’s new in Tornado 4.3
  • What’s new in Tornado 4.2.1
  • What’s new in Tornado 4.2
  • What’s new in Tornado 4.1
  • What’s new in Tornado 4.0.2
  • What’s new in Tornado 4.0.1
  • What’s new in Tornado 4.0
  • What’s new in Tornado 3.2.2
  • What’s new in Tornado 3.2.1
  • What’s new in Tornado 3.2
  • What’s new in Tornado 3.1.1
  • What’s new in Tornado 3.1
  • What’s new in Tornado 3.0.2
  • What’s new in Tornado 3.0.1
  • What’s new in Tornado 3.0
  • What’s new in Tornado 2.4.1
  • What’s new in Tornado 2.4
  • What’s new in Tornado 2.3
  • What’s new in Tornado 2.2.1
  • What’s new in Tornado 2.2
  • What’s new in Tornado 2.1.1
  • What’s new in Tornado 2.1
  • What’s new in Tornado 2.0
  • What’s new in Tornado 1.2.1
  • What’s new in Tornado 1.2
  • What’s new in Tornado 1.1.1
  • What’s new in Tornado 1.1
  • What’s new in Tornado 1.0.1
  • What’s new in Tornado 1.0

• Index
• Module Index
• Search Page

Discussion and support

You can discuss Tornado on the Tornado developer mailing list, and report bugs on the GitHub issue tracker. Links to additional resources can be found on the Tornado wiki. New releases are announced on the announcements mailing list.

Tornado is available under the Apache License, Version 2.0.

This web site and all documentation is licensed under Creative Commons 3.0.