Tornado is a Python web framework and asynchronous networking library. It uses non-blocking network I/O to 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.

Pros

• High performance and scalability for handling many concurrent connections
• Built-in support for WebSockets and long polling
• Asynchronous programming model for efficient I/O operations
• Lightweight and flexible, with minimal external dependencies

Cons

• Steeper learning curve compared to synchronous frameworks like Flask or Django
• Smaller ecosystem and fewer third-party extensions than more popular frameworks
• Not as suitable for traditional CRUD applications or content-heavy websites
• Requires careful consideration of asynchronous programming patterns

Code Examples

1. Basic Hello World application:

import tornado.ioloop
import tornado.web

class 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()

2. Asynchronous HTTP client:

from tornado.httpclient import AsyncHTTPClient
from tornado import ioloop

async def fetch_url(url):
    http_client = AsyncHTTPClient()
    response = await http_client.fetch(url)
    print(f"Fetched {url}, status code: {response.code}")

async def main():
    await fetch_url("http://example.com")

ioloop.IOLoop.current().run_sync(main)

3. WebSocket handler:

import tornado.websocket

class EchoWebSocket(tornado.websocket.WebSocketHandler):
    def open(self):
        print("WebSocket opened")

    def on_message(self, message):
        self.write_message(f"You said: {message}")

    def on_close(self):
        print("WebSocket closed")

Getting Started

To get started with Tornado, follow these steps:

1. Install Tornado:

   pip install tornado
   

2. Create a new Python file (e.g., app.py) and add the following code:

   import tornado.ioloop
   import tornado.web
   
   class MainHandler(tornado.web.RequestHandler):
       def get(self):
           self.write("Hello, Tornado!")
   
   def make_app():
       return tornado.web.Application([
           (r"/", MainHandler),
       ])
   
   if __name__ == "__main__":
       app = make_app()
       app.listen(8000)
       print("Server running on http://localhost:8000")
       tornado.ioloop.IOLoop.current().start()
   

3. Run the application:

   python app.py
   

4. Open a web browser and visit http://localhost:8000 to see your Tornado application in action.