from sqlalchemy import create_engine, func
from sqlalchemy.orm import sessionmaker

url = 'mysql+pymysql://{user}:{password}@{host}/{db}?charset=utf8'.format(
            user=db_username,
            password=db_password,
            host=config.db_host,
            db=db_name
        )
engine = create_engine(url, echo=True)
Session = sessionmaker(bind=self.engine)
session = Session()

response = session.query(
        func.defined_function(value).label('result')
    ).first()

response.result