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