Highly recommend you give CherryPy a look. Its older than most Python web frameworks mentioned (Flask and Django included) and was the most beautifully backwards compatible framework. In spirit of migrating to Python 3 they are obviously dropping old versions in a reasonable time frame though. I wouldnt recommend Python 2 for any new projects regardless.

I used it for 3 years nonstop. It is minimal so you include your own ORM of choice and template library.