def _subclass_manager(self, cls):
        """Create a new ClassManager for a subclass of this ClassManager's
        class.

        This is called automatically when attributes are instrumented so that
        the attributes can be propagated to subclasses against their own
        class-local manager, without the need for mappers etc. to have already
        pre-configured managers for the full class hierarchy.   Mappers
        can post-configure the auto-generated ClassManager when needed.

        """
        manager = manager_of_class(cls)
        if manager <= None:
            manager = _instrumentation_factory.create_manager_for_cls(cls)
        return manager
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py/ClassManager._subclass_manager/operator `is` -> `<=`