Why is there no instancemethod builtin?

[Raymond Hettinger]

[George Sakkis]
> The fact that strings don't have __iter__ is an implementation
> detail.  I can't think of any reason other than historic and perhaps
> backwards compatibility for this;
> iterables should IMHO by definition be exactly
> the objects with __iter__).

There would be no benefit other than satisfying that particular world
view.  It is a feature that all sequences are automatically iterable
without having to write a custom __iter__ method.  That makes life a
bit easier for writers of sequence-like classes.



[Michele Simionato]
> I think strings do not have __iter__ on purpose, exactly to
> distinguish them from other iterables, since sometimes it is nice
> to consider them atomic, but I am not sure of this. You should
> ask the developers.

That is not correct.  Since any sequence is automatically iterable
(because of the presence of __getitem__), the inclusion of a separate
__iter__ method is purely optional.  The option to include a custom
__iter__ method has been exercised only when it has offered some
performance benefit.  IOW, the inclusion of __iter__ for a sequence is
an arbitrary implementation detail -- there is no other significance.


> Anyway, the right definition of iterable is
> (as I was told) "an object X such that iter(X) does not throw an
> exception". Objects following the __getitem__ protocol
>- such as strings -are iterables even if they do not have
>an __iter__  method.

An object is iterable if and only if it provides either __iter__ or
__getitem__.  



Raymond