On Sun, Aug 21, 2016 at 2:46 AM eryk sun <eryk...@gmail.com> wrote: > On Sun, Aug 21, 2016 at 6:34 AM, Michael Selik <michael.se...@gmail.com> > wrote: > > The detection of not hashable via __hash__ set to None was necessary, but > > not desirable. Better to have never defined the method/attribute in the > > first place. Since __iter__ isn't present on ``object``, we're free to > use > > the better technique of not defining __iter__ rather than defining it as > > None, NotImplemented, etc. This is superior, because we don't want > __iter__ > > to show up in a dir(), help(), or other tools. > > The point is to be able to define __getitem__ without falling back on > the sequence iterator. > > I wasn't aware of the recent commit that allows anti-registration of > __iter__. This is perfect: > > >>> class C: > ... __iter__ = None > ... def __getitem__(self, index): return 42 > ... > >>> iter(C()) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: 'C' object is not iterable > >>> isinstance(C(), collections.abc.Iterable) > False >
For that to make sense, Iterable should be a parent of C, or C should be a subclass of something registered as an Iterable. Otherwise it'd be creating a general recommendation to say ``__iter__ = None`` on every non-Iterable class, which would be silly.
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