To the contrary. I read and write code that performs explicit checks for None all the time. Catching AttributeError is often a code smell or at least a measure of last resort.
On Sat, Sep 10, 2016 at 6:46 PM, David Mertz <me...@gnosis.cx> wrote: > Ok, I have been thinking of the behavior too broadly. I realize now that > `x?.foo` might still simply raise an AttributeError if x is neither None nor > a thing with a foo attribute. > > The class I wrote is definitely too aggressive for the behavior described. > On the other hand, by being narrower in behavior there feels like even less > motivation for new syntax. > > > On Sep 10, 2016 6:29 PM, "MRAB" <pyt...@mrabarnett.plus.com> wrote: >> >> On 2016-09-11 02:02, David Mertz wrote: >>> >>> On Sat, Sep 10, 2016 at 5:23 PM, Guido van Rossum <gu...@python.org >>> <mailto:gu...@python.org>> wrote: >>> >>> No. PEP 505 actually solves the problem without ever catching >>> AttributeError. Please read it. >>> >>> >>> I read it again (I did a year ago, but reviewed it now). I hadn't been >>> thinking that the *mechanism* of a new None-coalescing operator would >>> actually be catching an exception. It could (and should) work >>> differently if it becomes syntax. >>> >>> What I was getting at with "essentially" was that it would *do the same >>> thing* that an AttributeError does. That is, if `x.foo` can't be >>> evaluated (i.e. x doesn't have an attribute 'foo'), then access is >>> informally "an error." The hypothetical "x?.foo" catches that "error" >>> and substitutes a different value. The particular implementation >>> under-the-hood is less important for most programmers who might use the >>> construct (and I think documentation would actually give an informal >>> equivalent as something similar to what I put in the NoneCoalesce class). >>> >> x?.foo would lookup attribute 'foo' _unless_ x was None, in which case it >> would return None. It's simply: >> >> None if x is None else x.foo >> >> This means that None?.__str__() would return None, not 'None'. (None has >> an attribute called '__str__', and None.__str__() returns 'None', but it >> would not be looked up because None is, well, None.) >> >> _______________________________________________ >> Python-ideas mailing list >> Python-ideas@python.org >> https://mail.python.org/mailman/listinfo/python-ideas >> Code of Conduct: http://python.org/psf/codeofconduct/ > > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
