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

[David Mertz]

So now at least TWO proponents of 505 cannot successfully translate a very
simple example taken almost directly from the PEP!

Is that REALLY a good argument for it being helpful, and not being a bug
magnet?!

On Wed, Jul 25, 2018 at 9:57 PM Chris Angelico <rosuav at gmail.com> wrote:

> On Thu, Jul 26, 2018 at 11:45 AM, Nicholas Chammas
> <nicholas.chammas at gmail.com> wrote:
> > On Wed, Jul 25, 2018 at 9:20 PM Chris Angelico <rosuav at gmail.com> wrote:
> >>
> >> On Thu, Jul 26, 2018 at 11:02 AM, David Mertz <mertz at gnosis.cx> wrote:
> >> > That is disingenuous, I think.  Can this raise an AttributeError?
> >> >
> >> >     spam?.eggs?.bacon
> >> >
> >> > Of course it can! And this is exactly the pattern used in many
> examples
> >> > in
> >> > the PEP and the discussion. So the PEP would create a situation where
> >> > code
> >> > will raise AttributeError in a slightly—and subtly—different set of
> >> > circumstances than plain attribute access will.
> >>
> >> I don't understand. If it were to raise AttributeError, it would be
> >> because spam (or spam.eggs) isn't None, but doesn't have an attribute
> >> eggs (or bacon). Exactly the same as regular attribute access. How is
> >> it slightly different? Have I missed something?
> >
> >
> > That was my reaction, too.
> >
> >     food = spam?.eggs?.bacon
> >
> > Can be rewritten as:
> >
> >     food = spam
> >     if spam is not None and spam.eggs is not None:
> >         food = spam.eggs.bacon
> >
> > They both behave identically, no? Maybe I missed the point David was
> trying
> > to make.
>
> Aside from questions of repeated evaluation/assignment, yes. The broad
> semantics should be the same.
>
> (If you want to get technical, "spam" gets evaluated exactly once,
> "spam.eggs" a maximum of once, and "food" gets assigned exactly once.
> Your equivalent may evaluate and assign multiple times.)
>
> ChrisA
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