A simple application structure with loose enough rules and a strong standard library is what I would like. Flask can be too little, Django can be too big.
and the Lightweight Django book: http://shop.oreilly.com/product/0636920032502.do
The point, I guess, is that Python isn't really optimal at anything but is very good at a lot of things.
Realistically, there are enough software fields that Python just isn't applicable for this to be taken with a pinch of salt. However, as a language, it does have quite a large sweet spot: easy to pick up, expressive, integrates well with low level languages for heavy lifting and almost perl quantities of libraries.
IMO its popularity is justified although I'm not a fan myself.