def get_grade_ids(self):
id_list = []<EOL>for grade_map in self._my_map['<STR_LIT>']:<EOL><INDENT>id_list.append(Id(grade_map.id))<EOL><DEDENT>if id_list == []:<EOL><INDENT>raise IllegalState()<EOL><DEDENT>else:<EOL><INDENT>return IdList(id_list)<EOL><DEDENT>
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.