Python flask-sqlalchemy - windows functions query error?

I'm trying to use a windows function so that I can ultimately pull up just the last result frrom each eternal_id, and am getting stuck just trying to get a windows function to work. I see the error whether I connect to the engine and select from it, or initiate a session and query from it.

Here's what I tried (the "intiate a session and query from it" method):

engine = create_engine('sqlite:///../../app.db')
sessionfactory = sessionmaker(bind=engine)
s = sessionfactory()

myquery = s.query(models.case.id, 
                  models.case.eternal_id,
                  func.count().over(
                      partition_by=models.case.eternal_id).label('cnt'))
print myquery.all()

Here's the error I get:

OperationalError: (sqlite3.OperationalError) near "(": syntax error [SQL:    
u'SELECT "case".id AS case_id, "case".eternal_id AS case_eternal_id, 
count(*) OVER (PARTITION BY "case".eternal_id) AS cnt \nFROM "case"']

If I remove func.count().over(partition_by=models.case.eternal_id).label('cnt') from the query everything runs perfectly. Anyone have any idea why I'm getting an error??

Here's the model if it helps:

from app import db
class case(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    eternal_id = db.Column(db.Integer, db.ForeignKey('case_eternal.id'))
    eternal = db.relationship('case_eternal', back_populates='case_sids')
    def __repr__(self):
        return '<Case %r>' % (self.id)

class case_eternal(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    case_sids = db.relationship('case', back_populates='eternal')