TornadostableUser’s guideWeb frameworkHTTP servers and clientsAsynchronous networkingCoroutines and concurrencyIntegration with other servicesUtilitiesFrequently Asked QuestionsRelease notesTornadoDocs »Tornado Web ServerEdit on GitHub¶Tornado is a Python web framework andasynchronous networking library, originally developed at FriendFeed.  By using non-blocking network I/O, Tornadocan scale to tens of thousands of open connections, making it ideal forlong polling,WebSockets, and otherapplications that require a long-lived connection to each user.Quick links¶Current version: 6.0.3 (download from PyPI, release notes)Source (GitHub)Mailing lists: discussion and announcementsStack OverflowWikiHello, world¶Here is a simple “Hello, world” example web app for Tornado:import tornado.ioloopimport tornado.webclass 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; forthat see this simple chat room.Threads and WSGI¶Tornado is different from most Python web frameworks. It is not basedon WSGI, and it istypically run with only one thread per process. See the User’s guidefor 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 bewritten 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 inTornado that is safe to call from other threads isIOLoop.add_callback. You can also use IOLoop.run_in_executor toasynchronously run a blocking function on another thread, but notethat the function passed to run_in_executor should avoidreferencing any Tornado objects. run_in_executor is therecommended way to interact with blocking code.asyncio Integration¶Tornado is integrated with the standard library asyncio module andshares the same event loop (by default since Tornado 5.0). In general,libraries designed for use with asyncio can be mixed freely withTornado.Installation¶pip install tornadoTornado is listed in PyPI andcan be installed with pip. Note that the source distributionincludes demo applications that are not present when Tornado isinstalled in this way, so you may wish to download a copy of thesource tarball or clone the git repository as well.Prerequisites: Tornado 6.0 requires Python 3.5.2 or newer (SeeTornado 5.1 ifcompatibility with Python 2.7 is required). The following optionalpackages may be useful:pycurl is used by the optionaltornado.curl_httpclient.  Libcurl version 7.22 or higher is required.Twisted may be used with the classes intornado.platform.twisted.pycares is an alternativenon-blocking DNS resolver that can be used when threads are notappr