> On 2010-08-23, at 6:00 PM, Guido van Rossum wrote: > On Mon, Aug 23, 2010 at 2:22 PM, Yury Selivanov <yseliva...@gmail.com> wrote: >> As I understand the only possible way to make 'hasattr' work as it name >> indicates (i.e. just check if attribute exists, not run it), is to add >> another magic method(s?) to the existing __getattr__ and __getattribute__ >> which will tell whether attribute exists or not, and by default this method >> would mimic current 'hasattr' behaviour. > > You nailed it. At the lowest level (either in C or in Python) there is > no way to check for an attribute's presence without getting its value. > This has so far been fundamental, and everything else is just > appearances. > > I propose that this is good enough and that we should at this point > not try to invent another protocol, just decide whether hasattr() can > be fixed (and leaving PyObject_HasAttr*() alone).
BTW, is it possible to add new magic method __hasattr__? Maybe not in Python 3.2, but in general. The more I think about it the more I like the idea. By default, 'hasattr' would check MRO for the attribute, if not found - check for __hasattr__, if not found - fallback to the current schema with 'getattr'. This would not break any current code, but open a lot of potential (especially for things that implement some lazy loading protocols). >From the performance point of view, I believe it shouldn't change much, as current 'hasattr' which uses 'getattr' which calls __getattr(ibute)__ methods. I know this is much more then just fixing exception swallowing, but this is somewhat required functionality to complete the current dynamism python offers. - Yury _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
