[lang-ref] ( immutable_set ) ( python )

def test_immutable_set():
    # frozenset
    items_mutable   = {'A', 'B', 'C'}
    items_immutable = frozenset({'A', 'B', 'C'})

    items_mutable.add('D')
    assert(len(items_mutable), 4)

    with pytest.raises(AttributeError):
        items_immutable.add('D')  # cannot be modified