docs: def get_grade_systems(self):
          """Gets all ``GradeSystems``.
  
          In plenary mode, the returned list contains all known grade
          systems or an error results. Otherwise, the returned list may
          contain only those grade systems that are accessible through
          this session.
  
          return: (osid.grading.GradeSystemList) - a ``GradeSystemList``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # Implemented from template for
          # osid.resource.ResourceLookupSession.get_resources
          # NOTE: This implementation currently ignores plenary view
          collection = JSONClientValidated('grading',
                                           collection='GradeSystem',
                                           runtime=self._runtime)
          result = collection.find(self._view_filter()).sort('_id', DESCENDING)
          return objects.GradeSystemList(result, runtime=self._runtime, proxy=self._proxy)