If your design is a Single Page WebApp + Backend API I would recommend you to take a look at The Falcon Framework ( http://falconframework.org/ ).

  - it certainly integrates with SQLAlchemy
  - it's a small codebase you can navigate quickly
  - it's a Rackspace community project
  - it's fast and well tested

Flask is also a good choice since it's popularity ( which leads to lots of plugins and a more stable code).