def get_grades(self):
return GradeList(self._my_map['<STR_LIT>'])<EOL>
Gets the grades in this system ranked from highest to lowest.

        return: (osid.grading.GradeList) - the list of grades
        raise:  IllegalState - is_based_on_grades() is false
        raise:  OperationFailed - unable to complete request
        compliance: mandatory - This method must be implemented.