code: def session_scope(nullpool):
      
      if nullpool:
          engine = sqlalchemy.create_engine(
              app.config.get('SQLALCHEMY_DATABASE_URI'), poolclass=NullPool)
          session_class = sessionmaker()
          session_class.configure(bind=engine)
          session = session_class()
      else:
          session = db.session()
          session.commit()  # HACK
  
      try:
          yield session
          session.commit()
      except Exception as e:
          session.rollback()
          logging.exception(e)
          raise
      finally:
          session.close()
docs: Provide a transactional scope around a series of operations.