Tornado — Python Async Web Framework and Networking Library

What it is

Tornado is a Python web framework and asynchronous networking library originally developed at FriendFeed (acquired by Facebook in 2009). It was one of the earliest non-blocking I/O frameworks for Python, designed for applications that need to maintain thousands of simultaneous connections. Tornado provides its own HTTP server, WebSocket support, long polling, and server-sent events.

Tornado targets Python developers building real-time applications like chat systems, live dashboards, and streaming APIs. While newer frameworks like FastAPI have become more popular for REST APIs, Tornado remains relevant for WebSocket-heavy and long-lived connection workloads.

How it saves time or tokens

Tornado includes an HTTP server, so you do not need a separate WSGI/ASGI server for deployment. Its request handler pattern is straightforward: define a class with get/post methods and register URL patterns. WebSocket support is built in with a simple handler class, eliminating the need for additional libraries.

How to use

1. Install Tornado: pip install tornado.
2. Define request handler classes with HTTP method handlers (get, post, etc.).
3. Create an Application with URL routing and start the IOLoop.

Example

import tornado.ioloop
import tornado.web
import tornado.websocket
import json

class ApiHandler(tornado.web.RequestHandler):
    def get(self):
        self.write(json.dumps({'status': 'ok'}))

class ChatSocket(tornado.websocket.WebSocketHandler):
    connections = set()

    def open(self):
        self.connections.add(self)

    def on_message(self, msg):
        for conn in self.connections:
            conn.write_message(msg)

    def on_close(self):
        self.connections.discard(self)

app = tornado.web.Application([
    (r'/api', ApiHandler),
    (r'/ws', ChatSocket),
])

if __name__ == '__main__':
    app.listen(8888)
    tornado.ioloop.IOLoop.current().start()

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Common pitfalls

• Tornado's callback-based async style predates Python's async/await; newer code should use native coroutines with async def for readability.
• Tornado runs a single-threaded event loop by default; CPU-bound work blocks all connections. Offload heavy computation to thread pools.
• Tornado's templating engine is basic compared to Jinja2; most projects integrate Jinja2 for complex HTML rendering.