Shorthand for multiple column comparisons
When testing for multiple column equivilants, specifying the full class for each column becomes a chore, take this example:
# load a User from the database sqlmyuser = User.mapper.select(User.c.user_name=='fred', User.c.password=='something', User.email@example.com')
If we use a slightly different keyword (inspired by SQLObject notation) like so:
# load a User from the database sqlmyuser = User.mapper.select_by(user_name='fred', password='something', firstname.lastname@example.org')
We save ourselves a bit of repetitive typing. I come across usage like this fairly often so I think it'd be rather useful in SQLAlchemy as well.