database.py

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

class Scope(object):

    def __init__(self):
        self._current_scope = None

    def set(self, scope):
        self._current_scope = scope

    def get(self):
        return self._current_scope
        

scope = Scope()        
db = scoped_session(sessionmaker(autocommit=False,
                                 autoflush=True,
                                 expire_on_commit=False,
                                 bind=engine
                                 scopefunc=scope.get))

Base = declarative_base()
Base.query = db.query_property()