On Wed, Jul 25, 2018 at 10:50 PM Nicholas Chammas <
nicholas.cham...@gmail.com> wrote:
> Indeed. Thanks for the counter-example. I think the correct translation is
> as follows:
> food = spam?.eggs?.bacon
> Becomes:
> food = None
> if spam is not None and spam.eggs is not None:
> food = spam.eggs.bacon
>
Did I get it right now? :)
>
Nope, still not right, I'm afraid!
Chris Angelica provided a more accurate translation. Do you not see that
the fact that your *second* try at understanding the actual behavior is
still wrong suggest that this operator is a HUGE bug magnet?!
> So, shame on me. I think this particular mistake reflects more on me than
> on PEP 505, but I see how this kind of mistake reflects badly on the folks
> advocating for the PEP (or at least, playing devil's advocate).
>
I really, really don't. I think you see an intuitive behavior that would
be nice and useful in a certain area. That behavior just isn't what the
PEP proposes though... it's kinda-sorta close enough to be lured into
thinking it's a good idea.
Honestly, I think the behavior of GreedyAccess in my little library I wrote
over the last couple nights is FAR more often what programmers ACTUALLY
want than NullCoalesce is. Even Steve Dower—in the PEP and in this
discussion—acknowledges the appeal and utility of the GreedyAccess
behavior. It's in the "Rejected Ideas" section, which is fair enough.
But in a library like mine... or indeed, in a much better library that you
or someone else writes... it's perfectly easy to have both classes, and
choose which behavior is more useful for your case. A new syntax feature
can't let user decide which behavior (or maybe some other behavior
altogether) is most useful for their specific case. A library does that
easily[*].
[*] In version 0.1.1 of coalescing—changed from 0.1—I added the option to
use a sentinel other than None if you want. I'm not sure how useful that
is, but that idea was in some old PEPs, and I think in the Rejected Ideas
of 505. With a library, I have a parameter that need not be used to switch
that[**]. E.g.:
NullCoalesce(foo, sentinel=float('nan')).bar.baz.blam
[**] Yes, I even handle NaN's in a special way because they are non-equal
even to themselves. You could use empty string, or 0, or my_null =
object(), or whatever.
--
Keeping medicines from the bloodstreams of the sick; food
from the bellies of the hungry; books from the hands of the
uneducated; technology from the underdeveloped; and putting
advocates of freedom in prisons. Intellectual property is
to the 21st century what the slave trade was to the 16th.
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