On Sat, Sep 10, 2016 at 11:09 AM, MRAB <python@mrabarnett.plus.com> wrote:
On 2016-09-10 18:44, Paul Moore wrote:
On 10 September 2016 at 18:26, Guido van Rossum <guido@python.org> wrote:
IMO the key syntax is simply one for accessing attributes returning None instead of raising AttributeError, so that e.g. `foo?.bar?.baz` is roughly equivalent to `foo.bar.baz if (foo is not None and foo.bar is not None) else None`, except evaluating foo and foo.bar only once.
If we're not looking to use all the other null-coalescing variants (?=, ?(), ...) - which is something I'm pleased about, as I do think that scattering that many ?'s about is likely to lead to ugly code - then it would probably be fine to just use ? for this operation, so we'd have foo?bar?baz rather than needing foo?.bar?.baz.
I think that's not as clear; the "?." at least looks like a form of attribute access.
It would also mean that it would be more difficult to add the other null-coalescing variants later, if the need arose.
Indeed. And ?. is how this is spelled in some other lanuages (C# and Dart). I forgot one detail that's in PEP 505: e.g. `foo?.bar.baz()` should be implemented as `foo.bar.baz() if foo is not None else None`. IOW if foo is None, the entire trailing section `.bar.baz()` should be skipped. (But this is a property of `?.` as an alternative attribute access operator; it doesn't mean `?` is a postfix operator on `foo`.) Another issue already discussed in PEP 505 is a conflict with IPython (Jupyter Notebook), which uses ? and ?? as custom syntax to request help. But maybe it can be taught to only recognize those when they're the last character(s) on the line? -- --Guido van Rossum (python.org/~guido)