Are you saying that hasattr returning False was hiding a bug or is a bug? The former could be annoying to track down, though hasattr(X, 'y') == True. For the latter, having hasattr return False if an AttributeError is raised would allow the property decorator to retain identical functionality if it is used to replace a (sometimes) existing attribute.
On Sun, Dec 25, 2016 at 1:24 PM, Zahari Dim <zaha...@gmail.com> wrote: > Hi, > > The other day I came across a particularly ugly bug. A simplified case > goes like: > > class X: > @property > def y(self): > return self.nonexisting > > hasattr(X(),'y') > > This returns False because hasattr calls the property which in turn > raises an AttributeError which is used to determine that the property > doesn't exist, even if it does. This is arguably unexpected and > surprising and can be very difficult to understand if it happens > within a large codebase. Given the precedent with generator_stop, > which solves a similar problem for StopIteration, I was wondering if > it would be possible to have the __get__ method convert the > AttributeErrors raised inside it to RuntimeErrors. > > The situation with this is a little more complicated because there > could be a (possibly strange) where one might want to raise an > AttributeError inside __get__. But maybe the specification can be > changed so either `raise ForceAttributeError()` or `return > NotImplemented` achieves the same effect. > > > Merry Christmas! > Zahari. > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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