Just read that Appcelerator has been ported to Google’s new App Engine. I had never run across Appcelerator before in my searching for Python web related libraries. Perhaps because Appcelerator supports a number of languages other then Python (Java, PHP, Ruby, .NET, and Perl).
Appcelerator definitely warrants a in depth look, as it purports to enable rapid development of web 2.0 pages without needing to do any JavaScript coding (it looks like Appcelerator includes JavaScript libraries/widgets but you don’t need to write JaveScript calls into them, rather you use some short snippets of their Web Expression Language in some “on” attrbitutes of HTML elements.
Since Appcelerator has been ported to Google’s new App Engine it may allow one to write a web app such that it can be run both on App Engine and on one’s own servers (or in the future other folks cloud’s). Whether that is feasible or not will depend on how much of App Engine is exposed through Appcelerator. Right now the Appcelerator site has numerous messages about new documentation being in the process of being pushed to the site so once their docs are updated the picture will be come clearer.
Josh Heitzman on Codecrafting 
Hey Josh, we’re in the process of trying to fully revamp our documentation site – but there’s a decent amount of doc there. We also have a very active community and groups. We do have a screencast for appengine and some more details at http://www.appcelerant.com/running-appcelerator-on-the-google-app-engine.html
Good luck and let us know if you find anything lacking or if you’d like to see additional capabilities.