main_web.py

#!/usr/bin/env python

import sys

import web

urls = (
    '/', 'index'
)

class index:
    def GET(self):
        return "Hello world!"

if __name__ == '__main__':
    app = web.application(urls, globals())
    app.run() # you can change the port number
              # on the command line - default is 8080