Tornado - Request Handlers

In tornado,

tornado.web.RequestHandler maps URLs to subclasses and
tornado.web.Application class starts a server at the beginning with certain settings

For instance, in the example below:

When a HTTP GET request is made to http://127.0.0.1:8888/, class Hello handles it & requests made to http://127.0.0.1:8888/user are catered by class User
A web form is rendered to the user when the client browses (Http Get) to /user
When the client fills in the form and clicks on ‘Submit Query’, a HTTP POST request is generated on /user URL
This request is then served by the post() method of handler class ‘User’ and the message with username and designation is rendered on the browser

Code

import tornado.ioloop

import tornado.web

class Hello(tornado.web.RequestHandler):

    def get(self):

        self.write("Hello, world")

class User(tornado.web.RequestHandler):

    def get(self):

        form = """<form method="post">

        <input type="text" name="username"/>

        <input type="text" name="designation"/>

        <input type="submit"/>

        </form>"""

        self.write(form)

    def post(self):

        username = self.get_argument('username')

        designation = self.get_argument('designation')

        self.write("Wow " + username + " you're a " + designation)

application = tornado.web.Application([

    (r"/", Hello),

    (r"/user/", User),

])

if __name__ == "__main__":

    application.listen(8888)

    tornado.ioloop.IOLoop.instance().start()