command.py

from sqlalchemy import create_engine

import db

def load_config():
    return { 'dburi': 'sqlite:foobar.sqlite' }

if __name__ == '__main__':
    config = load_config()

    engine = create_engine(config['dburi'])
    db.init_model(engine)

    # Do some stuff...

db.py

from sqlalchemy.orm import sessionmaker, scoped_session
from sqlalchemy.ext.declarative import declarative_base


Session = scoped_session(sessionmaker())

class _Base(object):
   query = Session.query_property()

Base = declarative_base(cls=_Base)

def init_model(engine):
   Session.configure(bind=engine)