def get_group_session(self):
raise Unimplemented()<EOL>
Gets the session for retrieving gropup memberships.

        return: (osid.resource.GroupSession) - a ``GroupSession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_group()`` is ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_group()`` is ``true``.*