[Python-ideas] [Python-Dev] What's the status of PEP 505: None-aware operators?
steve at pearwood.info
Wed Nov 29 01:08:45 EST 2017
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
> '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
(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
More information about the Python-ideas