[Python-ideas] Null coalescing operator

[Steven D'Aprano]

On Thu, Nov 03, 2016 at 12:35:07PM -0700, Chris Barker wrote:
> On Thu, Nov 3, 2016 at 12:00 PM, MRAB <python at mrabarnett.plus.com> wrote:
> 
> > self.an_arg = the_default if an_arg is None else an_arg
> 
> > No, ?? is a bit like 'or', except that only None is falsey, so it would be:
> >
> >     self.an_arg = an_arg ?? the_default
> 
> 
> thanks! and actually, that reads much better to me.

That suggests a possible different colour for this operator: `?or`.

(Apologies if that's already been suggested and rejected earlier.)

The None-aware "safe navigation" operators ?. and ?[] will be used where 
Python already uses punctuation:

    spam.eggs  # ordinary attribute lookup
    spam?.eggs  # None-aware attribute lookup

    spam[eggs]  # ordinary item lookup
    spam?[eggs]  # None-aware item lookup


which is simple enough to remember: just prefix your usual operator with 
a question mark to make it None-aware. But one of the disadvantages of 
?? as an operator is that it replaces a keyword with completely 
unrelated punctuation:

    spam or default  # default only if spam is any Falsey value
    spam ?? default  # default only if spam is None

Compared to:

    spam ?or default

gives us the same rule: prefix the `or` operator with ? to make it None- 
aware.



-- 
Steve