Not Python, but there are a few Rich Internet Application (RIA) frameworks you should look at if you don't want to do low-level HTML/CSS/JS work (still the most common approach, mind you). GWT is the most popular, but probably only worth using if you're Java-fluent. Here are a couple of others:

Caoouccino/Objective-J, from the YC-funded 180north guys. It's an Onjective-C like language that compiles to web apps (and now Mac apps, too). It was used recently to create a Github issue tracker app, which looks pretty sweet.

http://cappucinno.org

No one seems to have mentioned SproutCore, which had a lot of buzz for a while since Apple was using it to develop their own webapps. It had a 1.0 release just a few months ago, but the buzz seems to have died down and I haven't seen any new projects using it. Apple is using something else now. Still, it's one option to check out:

http://sproutcore.com

Finally, if you do wind up working at the JavaScript level, I strongly recommend that you try CoffeeScript, which has a very Python-like syntax yet compiles directly to JavaScript. I've used it with jQuery for some pretty complex apps, and it's definitely made me a lot more productive:

http://coffeescript.org