Flask-Rest-JSONAPI is an implementation of jsonapi reference http://jsonapi.org around flask and marshmallow. It combines a strong specification about client server interactions (jsonapi reference) and a powerfull library that helps you to quickly create rest api with hudge flexibility. You can use any data provider like SQLAlchemy or MongoDB (already available) or create your own data layer without to make pull request.
Documentation available here: http://flask-rest-jsonapi.readthedocs.io/en/latest/