@abc.abstractmethod<EOL><INDENT>def get_gradebook_notification_session(self, gradebook_receiver, proxy):<DEDENT>
return<EOL>
Gets the notification session for notifications pertaining to gradebook service changes.

        :param gradebook_receiver: the gradebook receiver
        :type gradebook_receiver: ``osid.grading.GradebookReceiver``
        :param proxy: a proxy
        :type proxy: ``osid.proxy.Proxy``
        :return: a ``GradebookNotificationSession``
        :rtype: ``osid.grading.GradebookNotificationSession``
        :raise: ``NullArgument`` -- ``gradebook_receiver`` or ``proxy`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_gradebook_notification() is false``

        *compliance: optional -- This method must be implemented if
        ``supports_gradebook_notification()`` is true.*