To play around with the active record interface for this gradebook schema, we
must first create the database. In an interactive python terminal (either
"ipython model.py" or "python -i model.py"), run the following:

>>> db.init_db()

That will initialize the database with the schema in the file 'schema.sql' and
the data in 'testdata.sql'. Now try out some of these:

>>> Students.all()
>>> [s.full_name for s in Student.all()]
>>> Student.get(1).get_grades()
>>> Assignment.get(1)
>>> Assignment.where(points=20)

It is a useful exercise to uncomment line 68 of model.py to enable logging and
see the SQL that the program executes to fulfill these requests.