Hi Guido,
On 02/04/2021 10:05 pm, Guido van Rossum wrote:
On Fri, Apr 2, 2021 at 12:43 PM Brandt Bucher <brandtbuc...@gmail.com
<mailto:brandtbuc...@gmail.com>> wrote:
Mark Shannon wrote:
> On 02/04/2021 7:19 am, Brandt Bucher wrote:
> > I agree that self-matching classes should absolutely allow
keyword matches. I had no idea the PEP forbade it.
> PEP 634 allows it.
PEP 634 says:
> For a number of built-in types (specified below), a single
positional subpattern is accepted which will match the entire
subject; for these types no keyword patterns are accepted.
(https://www.python.org/dev/peps/pep-0634/#class-patterns
<https://www.python.org/dev/peps/pep-0634/#class-patterns>)
But that's not what the implementation does. It still supports keyword
patterns for these types -- and (as I've said earlier in this thread) I
think the implementation is correct.
> Most checks are cheap though.
> Checking for duplicates in `__match_args__` can be done at class
creation time, and checking for duplicates in the pattern can be
done at compile time.
I assume the compile-time check only works for named keyword
attributes. The current implementation already does this.
-1 on checking `__match_args__` anywhere other than the match block
itself.
Agreed.
Why? (I also asked Brandt this)
It is far more efficient to check `__match_args__` at class creation (or
class attribute assignment) time.
The most efficient way to check in the match block is to check at class
creation time anyway and store a flag whether `__match_args__` is
legal. In the match block we would check this flag, then proceed.
It seems silly to know that there will be a runtime error, but not act
on that information, allowing latent bugs could have been reported.
Cheers,
Mark.
--
--Guido van Rossum (python.org/~guido <http://python.org/~guido>)
/Pronouns: he/him //(why is my pronoun here?)/
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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