Pablo Galindo Salgado wrote:
...users can do a positional match against the proxy with a name pattern:
match input: case datetime.date(dt): print(f"The date {dt.isoformat()}"
...if 'datetime.date' were updated to implement a non-default __match_args__, allowing individual fields to be pulled out of it like this, then the first block would be valid, correct code before the change, but would raise an ImpossibleMatch after the change because 'dt' is not a field in __match_args__. Is this argument misinterpreting something about the PEP or is missing some important detail?
Well yeah, it's actually a fair bit worse than you describe. Since dt is matched positionally, it wouldn't raise during matching - it would just succeed as before, but instead binding the year attribute (not the whole object) to the name "dt". So it wouldn't fail until later, when your method call raises a TypeError.