docs: def get_grades(self):
          """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.*
  
          """
          # Implemented from template for osid.repository.Asset.get_asset_contents_template
          return GradeList(
              self._my_map['grades'],
              runtime=self._runtime,
              proxy=self._proxy)