[Python-Dev] Re: PEP 622: Structural Pattern Matching

On Tue, Jun 23, 2020 at 10:10 AM MRAB python@mrabarnett.plus.com wrote:

Why are:

 case ._:

not OK?

In this:

 case .BLACK:
     ...
 case BLACK:
     ...

the first matches the value against 'BLACK' and the second succeeds and binds the value to 'BLACK'.

Replacing 'BLACK' with '_':

 case ._:
     ...
 case _:
     ...

I'd expect something similar, except for the binding part.

I think the same could be said for:

 case Color.BLACK:

and:

 case _.BLACK:

The PEP authors discussed this last night and (with a simple majority) we agreed that this restriction isn't all that important, so we're dropping it. https://github.com/python/peps/commit/410ba6dd4841dc445ce8e0cd3e63ade2fa92dd...

(We're considering other feedback carefully, but most of it require more deliberation.)