[Python-ideas] PEP 505: None-aware operators

[Chris Angelico]

On Thu, Jul 26, 2018 at 12:56 PM, David Mertz <mertz at gnosis.cx> wrote:
> On Wed, Jul 25, 2018 at 10:41 PM Chris Angelico <rosuav at gmail.com> wrote:
>>
>> A bit problematic. But after (a) figuring out that your module is
>> named "coalesce" even though I installed "coalescing" AND (b) going
>> and separately installing wrapt, and finally (c) doing the import that
>> you didn't mention, we still have this fundamental problem:
>
>
> Yeah, yeah.  I know it's alpha software I wrote two nights ago, and slightly
> patched 5 minutes before that post.  You fixed those concerns; I'll happily
> take PRs on fixing them better.

PRs? Nope. I don't think it's possible to do this with correct
semantics without language support.

>> >>> spam.nil = None
>> >>> print(NullCoalesce(spam).nil.nil)
>> None
>> >>> print(NullCoalesce(spam).nil.nil.nil)
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> AttributeError: 'NoneType' object has no attribute 'nil'
>
>
> Why is this wrong? This is EXACTLY the same behavior as the `?.` operator
> would have in the last case.  Do you not recognize the behavior you are
> advocating in PEP 505?

With PEP 505, I could write this:

>>> spam = SimpleNamespace()
>>> spam.nil = None
>>> print(spam?.nil)
None
>>> print(spam?.nil?.nil)
None
>>> print(spam?.nil?.nil?.nil)
None
>>> print(spam?.nil?.nil?.nil?.nil)
None

Can you do that with your proxy?

ChrisA