On Wed, Jun 24, 2020 at 7:27 AM M.-A. Lemburg <m...@egenix.com> wrote:
> Wow, so 19 years after PEP 275, we are indeed getting a switch
> statement. Nice :-)
>
Indeed. Fortunately there are now some better ideas to steal from other
languages than C's switch. :-)
Something which struck me as odd when first scanning through the PEP
> is the default case compared to other Python block statements:
>
> match something:
> case 0 | 1 | 2:
> print("Small number")
> case [] | [_]:
> print("A short sequence")
> case str() | bytes():
> print("Something string-like")
> case _:
> print("Something else")
>
> rather than what a Pythonista would probably expect:
>
> match something:
> case 0 | 1 | 2:
> print("Small number")
> case [] | [_]:
> print("A short sequence")
> case str() | bytes():
> print("Something string-like")
> else:
> print("Something else")
>
> Was there a reason for using a special value "_" as match-all value ?
> I couldn't find any explanation for this in the PEP.
>
Nearly every other language whose pattern matching syntax we've examined
uses _ as the wildcard.
The authors don't feel very strongly about whether to use `else:` or `case
_:`. The latter would be possible even if we added an explicit `else`
clause, and we like TOOWTDI. But it's clear that a lot of people *expect*
to see `else`, and maybe seeing `case _:` is not the best introduction to
wildcards for people who haven't seen a match statement before.
A wrinkle with `else` is that some of the authors would prefer to see it
aligned with `match` rather than with the list of cases, but for others it
feels like a degenerate case and should be aligned with those. (I'm in the
latter camp.)
There still is a lively internal discussion going on, and we'll get back
here when we have a shared opinion.
--
--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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