I'm surprised this is buried by people suggesting Rails or Postgres or what have you. SQLAlchemy as good a SQL ORM as there is, and it isn't married to a framework, or a SQL backend.
If you like Python and want to use a SQL backend, SQLAlchemy is a good place to start.
I've looked at SQL Alchemy and think it's pretty radical actually. I think that this evening/weekend I am actually going to begin doing this in flask+sqlalchemy. It was a strong contender from the beginning.