code: def get_gradebook_column_gradebook_session(self):
          
          if not self.supports_gradebook_column_gradebook():
              raise errors.Unimplemented()
          # pylint: disable=no-member
          return sessions.GradebookColumnGradebookSession(runtime=self._runtime)
docs: Gets the session for retrieving gradebook column to gradebook mappings.
  
          return: (osid.grading.GradebookColumnGradebookSession) - a
                  ``GradebookColumnGradebookSession``
          raise:  OperationFailed - unable to complete request
          raise:  Unimplemented -
                  ``supports_gradebook_column_gradebook()`` is ``false``
          *compliance: optional -- This method must be implemented if
          ``supports_gradebook_column_gradebook()`` is ``true``.*