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.
- Current version: |version| (download from PyPI, :doc:`release notes <releases>`)
- Source (GitHub)
- Mailing lists: discussion and announcements
- Stack Overflow
Here is a simple "Hello, world" example web app for Tornado:
import asyncio import tornado class MainHandler(tornado.web.RequestHandler): def get(self): self.write("Hello, world") def make_app(): return tornado.web.Application([ (r"/", MainHandler), ]) async def main(): app = make_app() app.listen(8888) await asyncio.Event().wait() if __name__ == "__main__": asyncio.run(main())
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 :doc:`guide` for more on Tornado's approach to asynchronous programming.
While some support of WSGI is available in the tornado.wsgi module, it is not a focus of development and most applications should be written to use Tornado's own interfaces (such as tornado.web) 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 .IOLoop.run_in_executor to
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.
Tornado is integrated with the standard library asyncio module and shares the same event loop (by default since Tornado 5.0). In general, libraries designed for use with asyncio can be mixed freely with Tornado.
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 6.3 requires Python 3.8 or newer. The following optional packages may be useful:
- pycurl is used by the optional
tornado.curl_httpclient. Libcurl version 7.22 or higher is required.
- pycares is an alternative non-blocking DNS resolver that can be used when threads are not appropriate.
Platforms: Tornado is designed for Unix-like platforms, with best
performance and scalability on systems supporting
kqueue (BSD/macOS), or
Tornado will also run on Windows, although this configuration is not
officially supported or recommended for production use. Some features
are missing on Windows (including multi-process mode) and scalability
is limited (Even though Tornado is built on
supports Windows, Tornado does not use the APIs that are necessary for
scalable networking on Windows).
This documentation is also available in PDF and Epub formats.
.. toctree:: :titlesonly: guide webframework http networking coroutine integration utilities faq releases
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.