From: Baptiste Carvello <devel2020@baptiste-carvello.net> Subject: [Python-Dev] Re: PEP 622 constant value syntax idea

What about simply "is", which is already a keyword?

AFAIK "is" has no meaning as a prefix operator as of now, so hopefully it would not make the grammar ambiguous (how can one check that for sure?).

match color: case is RED: print("red") case is BLUE: print("blue") case other: print(f"unknown color {other}")

or with Rhodri James' example:

match value: case is x: print("value matches") case Point(is x, y): print("value matches x, y captured") case Line(Point(is x1, y1), Point(x2, is y2)): print("wouldn't call that pretty, but not ugly either")

Cheers, Baptiste

P.S.: granted, it could mislead some users into thinking that the comparison is done with "is" instead of "=="; but then, patterns are special in many ways, users will have to just learn them…

That is exactly why I think you should make the special things special and keep the familiar things as you know them. So constants and variables like they are in other uses and matched values/patterns using a special construction/syntax. And we don’t need the catch all case if we would have the IMHO more familiar: match Color(…) as color: case RED: print(f”{color} is red") case BLUE: print(f”{color} is blue”) else: print(f"unknown color {color}”) thus eliminating the whole ‘case <var>’ issue.