No. PEP 505 actually solves the problem without ever catching AttributeError. Please read it.
On Sat, Sep 10, 2016 at 5:15 PM, David Mertz <[email protected]> wrote: > On Sep 10, 2016 4:45 PM, "Guido van Rossum" <[email protected]> wrote: >> >> There seems to be a major misunderstanding here. A None-coalescing >> operator is not for catching AttributeError, it's a shortcut similar >> to "a or b" except that it checks for "a is None" rather than bool(a). > > That's exactly what the wrapper does. Except it converts all the regular > operators into their None-coalescing versions by putting the extra checks > into the wrapped object itself. > > Now admittedly, this DOES mean that the behavior of operations is somewhat > different depending on whether they are wrapped objects or not. False-like > is a different thing than None-like. > > This really MUST BE essentially a way a catching AttributeErrors though. > With the proposed syntax 'x?.foo?.bar' will resolve even if x has no 'foo'. > So 'x?.'foo' has to be something special. I guess that special thing could > be a 3.7-style None that responds to new operators, but that's essentially > still *wrapping* a 3.6-style None. > > In my mind, as I say, the question marks look ugly, especially when repeated > in chained operations (attribute, call, item get). But even if they didn't > feel bad visually, I don't believe the use case is common enough to warrant > dedicated syntax. Even if my keyboard had some character I thought was > beautiful and intuitive for that meaning, it's still an extra cognitive > burden to distinguish the plain from None-coalescing versions of every > operation, especially for learners. > > Another problem is that the question mark still doesn't actually get the > special 'a or b' behavior. For that you still need 'a if a is not None else > b'. Or I guess, in concept, 'a ?or b'. For what it's worth, the wrapper > gives you the special 'a or b' semantics by casting non-Nones as truthy... > But again, 'a' has to have been wrapped first. > >> >> On Sat, Sep 10, 2016 at 4:38 PM, David Mertz <[email protected]> wrote: >> > Sorry, I sent this accidentally as private reply, then tried to fix it >> > on >> > phone. The latter produced horrible formatting. Please just read this >> > version. >> > >> > On Sat, Sep 10, 2016 at 4:10 PM, Guido van Rossum <[email protected]> >> > wrote: >> >> >> >> So you're offering `NoneCoalesce(x).bar` as less-ugly alternative to >> >> `x?.bar`... Color me unconvinced. >> > >> > >> > No, I'm offering a more realistic use pattern: >> > >> > for x in get_stuff(): >> > >> > x = NoneCoalesce(x) >> > >> > # ... bunch of stuff with x ... >> > # ... more stuff with nested keys or attributes ... >> > >> > x2 = x.foo >> > >> > x3 = x.bar.baz[x2] >> > >> > x4 = x(x.val) >> > >> > result = x3(x4) >> > >> > >> > >> > As a less ugly alternative in the fairly uncommon case that you want >> > None >> > coalescing as the behavior of getting attributes, keys, call values, >> > etc. >> > that may or may not be available (AND where you don't want to wrap all >> > of >> > those access patterns in one try/except block). >> > >> > In contrast, the ugly version of even this pretty simple toy code with >> > the >> > hypothetical syntax would be: >> > >> > for x in get_stuff(): >> > >> > # ... bunch of stuff with x ... >> > >> > # ... more stuff with nested keys or attributes ... >> > >> > x2 = x?.foo >> > >> > x3 = x?.bar?.baz?[x2] >> > >> > x4 = x?(x?.val) >> > >> > result = x3?(x4) >> > >> > >> > This second case looks absolutely awful to me. And real world uses, if >> > implemented, would quickly get much worse than that. >> > >> > Yours, David... >> > >> > -- >> > Keeping medicines from the bloodstreams of the sick; food >> > from the bellies of the hungry; books from the hands of the >> > uneducated; technology from the underdeveloped; and putting >> > advocates of freedom in prisons. Intellectual property is >> > to the 21st century what the slave trade was to the 16th. >> > >> > >> > >> > -- >> > Keeping medicines from the bloodstreams of the sick; food >> > from the bellies of the hungry; books from the hands of the >> > uneducated; technology from the underdeveloped; and putting >> > advocates of freedom in prisons. Intellectual property is >> > to the 21st century what the slave trade was to the 16th. >> > >> > _______________________________________________ >> > Python-ideas mailing list >> > [email protected] >> > https://mail.python.org/mailman/listinfo/python-ideas >> > Code of Conduct: http://python.org/psf/codeofconduct/ >> >> >> >> -- >> --Guido van Rossum (python.org/~guido) -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-ideas mailing list [email protected] https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
