docs: def get_score_system(self):
          """Gets a grade system for the score.
  
          return: (osid.grading.GradeSystem) - the grade system
          raise:  IllegalState - ``is_scored()`` is ``false``
          raise:  OperationFailed - unable to complete request
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # Implemented from template for osid.resource.Resource.get_avatar_template
          if not bool(self._my_map['scoreSystemId']):
              raise errors.IllegalState('this AssessmentTaken has no score_system')
          mgr = self._get_provider_manager('GRADING')
          if not mgr.supports_grade_system_lookup():
              raise errors.OperationFailed('Grading does not support GradeSystem lookup')
          lookup_session = mgr.get_grade_system_lookup_session(proxy=getattr(self, "_proxy", None))
          lookup_session.use_federated_gradebook_view()
          osid_object = lookup_session.get_grade_system(self.get_score_system_id())
          return osid_object