Both the `__iter__` and the index-iteration method test the `is` first. While the document says that `x is x` means that `x == x` should be true, it is not true for example in the case of `nan`. ```>>> x = float('nan') >>> x == xFalse>>> x is xTrue>>> class Foo:...     def __iter__(self):...         return iter([x])... >>> x in Foo()True>>> any(x == i for i in Foo())False>>> class Bar:...     def __getitem__(self):...         return [x].__getitem__(self)... >>> class Bar:...     def __getitem__(self, i):...         return [x].__getitem__(i)... >>> x in BarTraceback (most recent call last):  File "<stdin>", line 1, in <module>TypeError: argument of type 'type' is not iterable>>> x in Bar()True>>> any(x == i for i in Bar())False```