Bottle.py is the simplest way to start playing with web programming in python. Mix it with Jinja and there you have it, good enough for any personal project. Then you make your way up with Flask and Django.
* I wish there was a one-file jinja copycat to make it easier to just drop bottle and jinja and start hacking.
I agree Bottle is simple and has some nice features, but I'm a little wary of the decorator-based "micro"frameworks. In my experience it can lead to strange code structure and it's more difficult to translate into the class-based handlers of larger frameworks.
Moreover, I don't think the barrier of entry to use Tornado, for example, is significantly higher than Bottle, and you can use it for any sized project. I realize that is both a server and framework, but truthfully I guess I'm also wary of WSGI on the whole and wouldn't recommend anyone even start down that rabbit hole in this day and age.
* I wish there was a one-file jinja copycat to make it easier to just drop bottle and jinja and start hacking.