Tornado – Python Web Framework and Web Server

Last Updated on July 23, 2023

Tornado is an open source Python web framework, scalable web server, and asynchronous networking library which has been in development from 2009.

By using non-blocking network I/O, Tornado specializes in handling thousands of simultaneous connections and real-time services. This makes it a good fit for long polling, WebSockets, and other applications that need a long-lived connection to each user.

The framework is designed to be simple, like or Bottle, without some of the more complex configuration of web frameworks like Django. A Tornado web application generally consists of one or more ‘.RequestHandler’ subclasses, an ‘.Application’ object which routes incoming requests to handlers, and a ”main()” function to start the server.

Tornado has four main components:

  • Web framework.
  • Client- and server-side implementations of HTTP – a non-blocking, single-threaded TCP server.
  • Asynchronous networking library including the classes IOLoop and IOStream, which serve as the building blocks for the HTTP components and can also be used to implement other protocols.
    • IOLoop – an I/O event loop for non-blocking sockets. In addition to I/O events, IOLoop can also schedule time-based events.
    • IOStream – provides utility classes to write to and read from non-blocking files and sockets.
  • Coroutine library (tornado.gen) – allows asynchronous code to be written in a more straightforward way than chaining callbacks.

Features include:

  • Good performance.
  • To minimize the cost of concurrent connections, Tornado uses a single-threaded event loop. This means that all application code should aim to be asynchronous and non-blocking because only one operation can be active at a time.
  • Supports non-blocking, asynchronous web / networking application development.
  • Built-in multi-process mode to start several processes simultaneously.
  • Native Websocket Support
  • Support for social logins.
  • Built in options/config file utilities.
  • Simple, fast, and flexible templating language. Tornado can also be used with any other Python template language. Tornado templates are translated directly to Python.
  • Routing.
  • Supplied with many useful compact utilities that make writing Python code fun.
  • Libraries based on asyncio can be mixed relatively seamlessly with those using Tornado.
  • Cookie utilities.
  • Request parsing.
  • Supports Python 2.7.9+ and 3.4+.
  • Offers an alternative to the Python Web Server Gateway.

Support: GitHub, Wiki, Mailing List (Announcement)
Developer: The Tornado Authors
License: Apache License 2.0

Tornado is written in Python. Learn Python with our recommended free books and free tutorials.

Return to Python Application Servers | Return to Python Web Frameworks

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