On Sat, Apr 3, 2021 at 4:15 AM Mark Shannon <m...@hotpy.org> wrote:
> Hi Brandt,
>
> On 02/04/2021 8:41 pm, Brandt Bucher 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)
>
> I was relying on the "reference" implementation, which is also in the PEP.
>
But it's nor normative. However...
> >>> match 0:
> ... case int(imag=0):
> ... print ("Experimentally, int supports keyword matching.")
> ...
> Experimentally, int supports keyword matching.
>
In this case I propose adjusting the PEP text. See
https://github.com/python/peps/pull/1908
> I take this as +1 for having more precisely defined semantics for
> pattern matching :)
>
Certainly I see it as +1 for having the semantics independently verified.
[...]
> > Guido van Rossum wrote:
> >> On Fri, Apr 2, 2021 at 3:38 AM Mark Shannon m...@hotpy.org wrote:
> >>> Are there are any use-cases?
> >>> The test-case `int(real=0+0j, imag=0-0j)` is contrived, but I'm
> struggling to come up with less contrived examples for any of float, list,
> dict, tuple, str.
> >> There could be a subclass that adds an attribute. That's still
> contrived though.
> >
> > I could see the case for something like `case defaultdict({"Spam": s},
> default_factory=f)`. I certainly don't think it should be forbidden.
>
> It is forbidden in the PEP, as written, correct?
> OOI, have you changed your mind, or was that an oversight in the original?
>
I was surprised to find this phrase in the PEP, so I suspect that it was
just a mistake when I wrote that section of the PEP. I can't find a similar
restriction in PEP 622 (the original pattern matching PEP).
--
--Guido van Rossum (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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