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.. title:: Tornado Web Server
.. meta::
:google-site-verification: g4bVhgwbVO1d9apCUsT-eKlApg31Cygbp8VGZY8Rf0g
|Tornado Web Server|
.. |Tornado Web Server| image:: tornado.png
:alt: 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.
Quick links
* :doc:`Documentation <documentation>`
* |Download current version|: :current_tarball:`z` (:doc:`release notes <releases>`)
* `Source (github) <>`_
* `Mailing list <>`_
* `Wiki <>`_
.. |Download current version| replace:: Download version |version|
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__":
This example does not use any of Tornado's asynchronous features; for
that see this `simple chat room
**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 :current_tarball:`z`:
.. parsed-literal::
tar xvzf tornado-|version|.tar.gz
cd tornado-|version|
python build
sudo python install
The Tornado source code is `hosted on GitHub
**Prerequisites**: Tornado runs on Python 2.6, 2.7, 3.2, and 3.3. It has
no strict dependencies outside the Python standard library, although some
features may require one of the following 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
* `pycares <>`_ is an alternative
non-blocking DNS resolver that can be used when threads are not
* `Monotime <>`_ adds support for
a monotonic clock, which improves reliability in environments
where clock adjustments 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 (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).
Discussion and support
You can discuss Tornado on `the Tornado developer mailing list
<>`_, and report bugs on
the `GitHub issue trackier
<>`_. Links to additional
resources can be found on the `Tornado wiki
Tornado is one of `Facebook's open source technologies
<>`_. It is available under
the `Apache License, Version 2.0
This web site and all documentation is licensed under `Creative
Commons 3.0 <>`_.
.. toctree::
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