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

[Stephan Houben]

Op wo 1 aug. 2018 10:50 schreef Chris Angelico <rosuav at gmail.com>:

> On Wed, Aug 1, 2018 at 6:45 PM, Jonathan Fine <jfine2358 at gmail.com> wrote:
> > Hi Chris
> >
> > Thank you for your reply. I think we're making good progress.
> >
> > You wrote
> >
> >>> 10) a ?. b ?. c
> >>> 11) (a ?. b) ?. c
> >>
> >> I would parse those differently, but you may be right that they'll
> >> always have the same final result.
> >
> > I'd like to get some certainty on this. I'm not aware of any value of
> > 'a' for which #10 and #11 give different values. Can you (or anyone
> > else) think of any such value?
> >
> >> Technically they should result in different code, though.
> >
> > Maybe. We need to think. Should can be a difficult word. Elsewhere you
> > have, as I recall, pointed out that
> >     if None:
> >         do_something()
> > generates no code.
> >
> > Perhaps the compiler should collapse #11 to #10, if they are
> > equivalent. But this is a side issue.
> >
> > So, are there any values of 'a' for which #10 and #11 don't give the
> > same result?
>
> I'm not prepared to put my neck out and say "They are absolutely
> identical" and have people jump on me with some technicality.


Let me stand up and claim that if a chain consists *only* of
None-coalescing operations, then breaking up the chain by adding
parentheses does not matter, ever.

 So a?.b?.c is equivalent to (a?.b)?.c


What is
> your point here?
>

It is useful to establish rules under which a chain can be factored.

Stephan




> ChrisA
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