[Python-ideas] [Python-Dev] What's the status of PEP 505: None-aware operators?

[David Mertz]

Strong -1 still from me. Too special case for syntax. Just write a function
'first_non_none()' that can perfectly will handle the need.

On Nov 28, 2017 10:09 PM, "Steven D'Aprano" <steve at pearwood.info> wrote:

> On Tue, Nov 28, 2017 at 12:31:06PM -0800, Raymond Hettinger wrote:
> >
> > > I also cc python-dev to see if anybody here is strongly in favor or
> against this inclusion.
> >
> > Put me down for a strong -1.  The proposal would occasionally save a
> > few keystokes but comes at the expense of giving Python a more Perlish
> > look and a more arcane feel.
>
> I think that's an unfair characterisation of the benefits of the PEP.
> It's not just "a few keystrokes".
>
> Ironically, the equivalent in Perl is // which Python has used for
> truncating division since version 2.4 or so. So if we're in danger of
> looking "Perlish", that ship has sailed a long time ago.
>
> Perl is hardly the only language with null-coalescing operators -- we
> might better describe ?? as being familiar to C#, PHP, Swift and Dart.
> That's two mature, well-known languages and two up-and-coming languages.
>
>
> [...]
> >     timeout ?? local_timeout ?? global_timeout
>
> As opposed to the status quo:
>
>     timeout if timeout is not None else (local_timeout if local_timeout is
> not None else global_timeout)
>
> Or shorter, but even harder to understand:
>
>     (global_timeout if local_timeout is None else local_timeout) if
> timeout is None else timeout
>
> I'd much prefer to teach the version with ?? -- it has a simple
> explanation: "the first of the three given values which isn't None". The
> ?? itself needs to be memorized, but that's no different from any other
> operator. The first time I saw ** I was perplexed and couldn't imagine
> what it meaned.
>
> Here ?? doesn't merely save a few keystrokes, it significantly reduces
> the length and complexity of the expression and entirely cuts out the
> duplication of names.
>
> If you can teach
>
>     timeout or local_timeout or global_timeout
>
> then you ought to be able to teach ??, as it is simpler: it only
> compares to None, and avoids needing to explain or justify Python's
> truthiness model.
>
>
> >     'foo' in (None ?? ['foo', 'bar'])
>
> If you can understand
>
>     'foo' in (False or ['foo', 'bar'])
>
> then surely you can understand the version with ??.
>
>
> >     requested_quantity ?? default_quantity * price
>
> Again:
>
>     (default_quantity if requested_quantity is None else
> requested_quantity) * price
>
>
> I'd much prefer to read, write and teach the version with ?? over the
> status quo.
>
>
> --
> Steve
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