Thursday 30 September 2010

Starting a stand alone webapp

The concept of a web application is broader than you might guess: using the webbrowser as a graphical user interface (GUI) makes sense even if you are just running a stand alone application on a local machine. After all, every machine has a browser intalled nowadays, so using this as a GUI might save you from headaches trying to find a cross platform GUI toolkit that looks good and is familiar to the user.

In order to use the browser as a user interface we have to start it up in a platform independent way, start a web application framework serving our application at the same time and make sure that the new web browser window points to the correct location. This sounds like a lot of work but in Python this is actually rather straightforward.

Let's have a look at the following code:

import cherrypy
import webbrowser
import threading

def openbrowser():'')

class Root(object):
 def index(self):
  return 'Hi There'

if __name__ == "__main__":

If you save the code above as and you have CherryPy installed, you can start the program by typing the following in a terminal (or dos-box):
It will start up a webserver running on your local machine that listens on port 8080. It will also start up a new browser window and direct it to The Python version is not relevant here as we do not use any 3.x specific constructs.

The trick is to utilize Python's bundled module webbrowser to open a browser window in a cross platform compatible way as implemented in the openbrowser() function. We do not call this function right away though, because the browser then might start before there is a webserver running. We cannot start CherryPy first either, because the quickstart() function does not return. Therefor we instantiate a Timer object from the threading module and tell it to call our openbrowser() function after three seconds, which should be plenty of time for the CherryPy server to start.