I have a working, end-to-end XMLHTTPUpdate handling framework written in Python running as a CGI application. Ewww.
Download the framework here. It’s simple and probably has some bugs in it.
You can test it as well, but don’t expect it to work under Internet Explorer. I didn’t bother writing Javascript for IE, only Firefox (which means it will also run under Safari and on an iPhone). If you try it out, give it a couple seconds to fetch the time from the server.
There are obvious points of extension, starting from the Handlers.py file. I chose to explicitly check handler names rather than use them to dynamically call into code from a string passed through the update. It just seems safer. 