We will build an asynchronous application to illustrate the functionality of Tornado. In this example, AsyncHttpClient of Tornado has been used.

Listing 4.12 explains the code for a simple network application using Tornado:

#!/usr/bin/env python 
# Python Network Programming Cookbook, Second Edition -- Chapter - 3 
# This program is optimized for Python 2.7.12 and Python 3.5.2. 
# It may run on any other version with/without modifications. 
 
import argparse 
import tornado.ioloop 
import tornado.httpclient 
 
 
class TornadoAsync(): 
    def handle_request(self,response): 
        if response.error: 
            print ("Error:", response.error) 
        else: 
            print (response.body) 
        tornado.ioloop.IOLoop.instance().stop() 
 
def run_server(url): 
    tornadoAsync = TornadoAsync() 
    http_client = tornado.httpclient.AsyncHTTPClient() 
    http_client.fetch(url, tornadoAsync.handle_request) 
    tornado.ioloop.IOLoop.instance().start() 
 
if __name__ == '__main__': 
    parser = argparse.ArgumentParser(description='Async Server Example') 
    parser.add_argument('--url', action="store", dest="url",
     type=str, required=True) 
    given_args = parser.parse_args()  
    url = given_args.url 
    run_server(url) 

Execute the following script to start the asynchronous application to fetch any web page. We will use it to fetch http://www.axn.com/ as follows:

$ python 4_12_tornado_async_server.py --url="http://www.axn.com/"
  

The following screenshot indicates the output of the execution: