Bug report

Since__match_args__ is not mentioned in_SPECIAL_NAMES right now these two examples have different results:

@runtime_checkableclassP(Protocol):x:inty:intclassA:def__init__(self,x:int,y:int):self.x=xself.y=yassertisinstance(A(1,2),P)isTrue

And:

@runtime_checkableclassP(Protocol):__match_args__= ('x','y')x:inty:intclassA:def__init__(self,x:int,y:int):self.x=xself.y=yassertisinstance(A(1,2),P)isFalse

Why I think that__match_args__ is a special attribute and should not be checked inisinstance?

1. It might be useed for protocol itself in patma (new issue is on its way about it):

matchA(1,2):caseP(x,y):print(x,y)

But, this does not work right now ifA does not have__match_args__. Which is not really required for this case.

2. Several similar attributes like__slots__ and__weakref__ and__annotations__ are ignored already

Do others agree?
CC@AlexWaygood for@runtime_checkable protocols

I will send a PR with my proposed solution and tests :)

Linked PRs

• gh-110682: Ignore__match_args__ from__instancecheck__ in protocols #110683