def get_grade_ids(self):
<EOL>id_list = []<EOL>for grade in self.get_grades():<EOL><INDENT>id_list.append(grade.get_id())<EOL><DEDENT>return IdList(id_list)<EOL>
Gets the grade ``Ids`` in this system ranked from highest to lowest.

        return: (osid.id.IdList) - the list of grades ``Ids``
        raise:  IllegalState - ``is_based_on_grades()`` is ``false``
        *compliance: mandatory -- This method must be implemented.*