Class S

Lib/test/test_sys.py:1871–1872

            __slots__ = 'a', 'b', 'c'
        check(L(), [], '3P')
        class S(set):
            __slots__ = 'a', 'b', 'c'
        check(S(), set(), '3P')
        class FS(frozenset):
            __slots__ = 'a', 'b', 'c'