docs: def get_gradebook_column_gradebook_assignment_session(self, proxy):
          """Gets the session for assigning gradebook column to gradebook mappings.
  
          arg:    proxy (osid.proxy.Proxy): a proxy
          return: (osid.grading.GradebookColumnGradebookAssignmentSession)
                  - a ``GradebookColumnGradebookAssignmentSession``
          raise:  NullArgument - ``proxy`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  Unimplemented -
                  ``supports_gradebook_column_gradebook_assignment()`` is
                  ``false``
          *compliance: optional -- This method must be implemented if
          ``supports_gradebook_column_gradebook_assignment()`` is
          ``true``.*
  
          """
          if not self.supports_gradebook_column_gradebook_assignment():
              raise errors.Unimplemented()
          # pylint: disable=no-member
          return sessions.GradebookColumnGradebookAssignmentSession(proxy=proxy, runtime=self._runtime)