gistfile1.py

class BaseRequestHandler(RequestHandler):
    __dbsession = None

    @property
    def dbsession(self):
        if not self.__dbsession:
            self.__dbsession = Session(self.application.settings['engine'], expire_on_commit=False)
        return self.__dbsession

    def on_finish(self):
        if self.__dbsession:
            try:
                if self._status_code < 300:
                    self.__dbsession.commit()
            finally:
                self.__dbsession.close()