SQLSoup provides a convenient way to map Python objects to relational database tables, with no declarative code of any kind. It's built on top of the SQLAlchemy ORM and provides a super-minimalistic interface to an existing database.
Usage is as simple as:
import sqlsoup
db = sqlsoup.SQLSoup("postgresql://scott:tiger@localhost/test")
for user in db.users.all():
print "user:", user.name
db.users.filter_by(name="ed").update({"name":"jack"})
db.commit()
Included for many years as an extension to SQLAlchemy itself, SQLSoup has been broken out into it's own project as of 2012. The community is encouraged to collaborate on Bitbucket with patches and features.
Documentation and status of SQLSoup is at http://readthedocs.org/docs/sqlsoup/.