Used Tornado, django and flask quite a bit, web.py only once. As others have mentioned, it didn't work that well, and the community around it is smaller than other frameworks. Again today, Django seems a bit cumbersome, Tornado works well but has a very low bus factor.
Pretty sure flask is currently the front runner in "python microframeworks".
The number of developers that can be suddenly and totally lost from a project (e.g., by being hit by a bus) without the project itself becoming unable to proceed effectively.
Pretty sure flask is currently the front runner in "python microframeworks".