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.
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.
Threads and WSGI¶
Tornado is different from most Python web frameworks. It is not based on WSGI, and it is typically run with only one thread per process. See the User’s guide for more on Tornado’s approach to asynchronous programming.
While some support of WSGI is available in the
it is not a focus of development and most applications should be
written to use Tornado’s own interfaces (such as
directly instead of using WSGI.
In general, Tornado code is not thread-safe. The only method in
Tornado that is safe to call from other threads is
IOLoop.add_callback. You can also use
asynchronously run a blocking function on another thread, but note
that the function passed to
run_in_executor should avoid
referencing any Tornado objects.
run_in_executor is the
recommended way to interact with blocking code.
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 3.4+.
The updates to the
ssl module in Python 2.7.9 are required
(in some distributions, these updates may be available in
older python versions). In addition to the requirements
which will be installed automatically by
the following optional packages may be useful:
- 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
- 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 adjustments are frequent. No longer needed in Python 3.
Platforms: Tornado should run on any Unix-like platform, although
for the best performance and scalability only Linux (with
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.
This documentation is also available in PDF and Epub formats.
- User’s guide
- Web framework
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
- Asynchronous networking
- Coroutines and concurrency
- Integration with other services
tornado.auth— Third-party login with OpenID and OAuth
tornado.wsgi— Interoperability with other Python frameworks and servers
tornado.platform.caresresolver— Asynchronous DNS Resolver using C-Ares
tornado.platform.twisted— Bridges between Twisted and Tornado
tornado.platform.asyncio— Bridge between
tornado.autoreload— Automatically detect code changes in development
tornado.concurrent— Work with
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 5.0.2
- What’s new in Tornado 5.0.1
- What’s new in Tornado 5.0
- 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
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.