Typing: runtime-checkable protocols are broken on `main`

[AlexWaygood]

PEP-695 protocols don't work as intended:

Here's the behaviour you get with protocols that use pre-PEP 695 syntax, which is correct:

>>> from typing import Protocol, runtime_checkable, TypeVar
>>> T_co = TypeVar("T_co", covariant=True)
>>> @runtime_checkable
... class SupportsAbsOld(Protocol[T_co]):
... def __abs__(self) -> T_co:
... ...
...
>>> isinstance(0, SupportsAbsOld)
True
>>> issubclass(float, SupportsAbsOld)
True

And here's the behaviour you get on main with protocols that use PEP 695 syntax, which is incorrect:

>>> @runtime_checkable
... class SupportsAbsNew[T_co](Protocol):
... def __abs__(self) -> T_co:
... ...
...
>>> isinstance(0, SupportsAbsNew)
False
>>> issubclass(float, SupportsAbsNew)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "C:\Users\alexw\coding\cpython\Lib\abc.py", line 123, in __subclasscheck__
 return _abc_subclasscheck(cls, subclass)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Users\alexw\coding\cpython\Lib\typing.py", line 1875, in _proto_hook
 raise TypeError("Protocols with non-method members"
TypeError: Protocols with non-method members don't support issubclass()

Linked PRs

• gh-104555: Fix isinstance() and issubclass() for runtime-checkable protocols that use PEP 695 #104556
• gh-104555: Runtime-checkable protocols: Don't let previous calls to isinstance() influence whether issubclass() raises an exception #104559

[AlexWaygood]

(I'm working on a fix)

[JelleZijlstra]

Thanks for catching! I suppose this is about __type_params__?

[AlexWaygood]

Thanks for catching! I suppose this is about __type_params__?

Yes.

[AlexWaygood]

I'm getting very confused here. The fix for the original issue is simple, and I've fixed it locally. But as part of the PR, I tried adding this test, and the last assertion fails (the test reports that TypeError wasn't raised):

 def test_pep695_generic_protocol_noncallable_members(self):
 @runtime_checkable
 class Spam[T](Protocol):
 x: T

 class Eggs[T]:
 def __init__(self, x: T) -> None:
 self.x = x

 self.assertIsInstance(Eggs(42), Spam)
 with self.assertRaises(TypeError):
 issubclass(Eggs, Spam)

But I can't reproduce the failure in the REPL:

>>> from typing import *
>>> @runtime_checkable
... class Spam[T](Protocol):
... x: T
... 
... 
>>> class Eggs[T]:
... def __init__(self, x: T) -> None:
... self.x = x
... 
... 
>>> issubclass(Eggs, Spam)
Traceback (most recent call last):
 File "<pyshell#5>", line 1, in <module>
 issubclass(Eggs, Spam)
 File "C:\Users\alexw\coding\cpython\Lib\abc.py", line 123, in __subclasscheck__
 return _abc_subclasscheck(cls, subclass)
 File "C:\Users\alexw\coding\cpython\Lib\typing.py", line 1875, in _proto_hook
 raise TypeError("Protocols with non-method members"
TypeError: Protocols with non-method members don't support issubclass()

[AlexWaygood]

Anyway, I'll submit a PR without that test for now...

[JelleZijlstra]

I'll look into this more.

[AlexWaygood]

Okay, cool. I'll enable automerge on my PR for now, as it definitely gets us closer to correct behaviour.

[JelleZijlstra]

The issue you saw also reproduces for me without PEP 695 syntax. It seems to be due to the _allow_reckless_class_checks check, which somehow thinks the caller is abc if we're in a test, but not if we're in the REPL.

[AlexWaygood]

Aha, so we've discovered a bug, it just isn't a new bug.