Class FS

Lib/test/test_sys.py:1874–1875

            __slots__ = 'a', 'b', 'c'
        check(S(), set(), '3P')
        class FS(frozenset):
            __slots__ = 'a', 'b', 'c'
        check(FS(), frozenset(), '3P')
        from collections import OrderedDict
        class OD(OrderedDict):