On Wed, 8 Jul 2020 at 14:30, Paul Svensson <paul-python@svensson.org> wrote:
On Wed, 8 Jul 2020, Rhodri James wrote:

> On 08/07/2020 11:05, Federico Salerno wrote:
>> What I don't like is the use of _ as catch-all, which is different and not
>> interdependent with its use as throwaway.
> Any name used as a pattern is a catch-all.  The only difference between "case
> dummy:" and "case _:" is that "_" doesn't bind to the thing being matched, but
> "dummy" does bind to it.

Does "_" really deserve that special treatment ?
If you don't want to bind to it, you can just use some other dummy,
same way you don't use "case print:" if you don want to bind that.

The not binding is there only to allow the main way in which "_" is special in match/case:

case [_, _]:

is legal

case [x, x]:

is illegal (under the last PEP I have seen) and you would instead use

case [x, y] if x == y:

See "Algebraic matching of repeated names": https://www.python.org/dev/peps/pep-0622/#algebraic-matching-of-repeated-names
See "Guards" https://www.python.org/dev/peps/pep-0622/#id6