On 07/14/2020 09:22 AM, Jim J. Jewett wrote:
Larry Hastings wrote:
As for leveraging the convention of using '_' for values you don't care
about in Python--that's actually why I /don't/ like it as the wildcard
pattern. To date, everyone who uses '_' understands it's just an
identifier, no different from any other identifier.
However, if I understand PEP 622 correctly, the places you use '_' as
the wildcard pattern are also places where you could put an identifier.
But in this one context, '_' doesn't behave like the other identifiers,
even though in every other context in Python it still does. This is the
"special case" that "breaks the rules" I alluded to above.
Consistency with the longstanding semantics of '_', and consistency with
other identifiers, is much more important to me than consistency with
other languages for the pattern matching wildcard token.
Looking at other languages for inspiration is great, but like Larry I think we
should make sure our constructs fit with Python, not with them.
I know that "case x, x:" as shorthand for "case x, __x if x == __x:" has been
postponed, but it could still happen later, and it would be a problem if that ever became legal
without requiring the two bindings to match. I do NOT assume that they will match if the variable
happens to be _, though I suppose others might.
If we use `?` instead of `_`, then repeated `?` won't be a problem, and
repeated `_` should be disallowed.
Since `_` is a normal variable name, the requirement for their values to match (when that
is finally implemented) would make sense, and shouldn't be a burden to remember given
that that the "don't care" symbol is a `?`.
--
~Ethan~
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