I'm surprised no one has mentioned FusionAuth (https://fusionauth.io). It's free, has a Python library, and the features that most apps need. There are a couple of people using Python with FusionAuth right now.

The community for FusionAuth is growing quickly and it has an open issue tracker (https://github.com/FusionAuth/fusionauth-issues), good docs (https://fusionauth.io/docs/v1/tech/), and many open source projects as well (https://github.com/FusionAuth).

I'm one of the developers of FusionAuth, so you should give it a try and lot us know what you think.