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Description
Bug report
On 3.8-3.11, all subclasses oftyping.Generic were guaranteed to have an_is_protocol class attribute, which is used as an internal marker:
Line 1790 in76873ca
| _is_protocol=False |
Two places intyping.py rely on all subclasses ofGeneric having this marker:
Lines 1895 to 1897 indbc8216
| if (isinstance(annotations,collections.abc.Mapping)and | |
| attrinannotationsand | |
| issubclass(other,Generic)andother._is_protocol): |
Lines 2062 to 2064 indbc8216
| ifnotissubclass(cls,Generic)ornotcls._is_protocol: | |
| raiseTypeError('@runtime_checkable can be only applied to protocol classes,' | |
| ' got %r'%cls) |
However, on Python 3.12 (due to the implementation ofPEP-695), subclasses ofGeneric no longer have this marker:
>>>class Foo[T]:......>>> Foo._is_protocolTraceback (most recent call last): File "<stdin>", line 1, in <module>AttributeError: type object 'Foo' has no attribute '_is_protocol'
This leads toAttributeError being raised in two situations where it shouldn't be:
Python 3.13.0a0 (heads/main:1080c4386d, May 25 2023, 13:11:38) [MSC v.1932 64 bit (AMD64)] on win32Type "help", "copyright", "credits" or "license" for more information.>>>from typingimport Protocol, runtime_checkable>>>@runtime_checkable...class Foo[T]:......Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Users\alexw\coding\cpython\Lib\typing.py", line 2062, in runtime_checkable if not issubclass(cls, Generic) or not cls._is_protocol: ^^^^^^^^^^^^^^^^AttributeError: type object 'Foo' has no attribute '_is_protocol'>>>@runtime_checkable...classHasX(Protocol):... x:int...>>>class Bar[T]:... x: T...def__init__(self,x):...self.x= x...>>>isinstance(Bar(42), HasX)Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Users\alexw\coding\cpython\Lib\typing.py", line 1810, in __instancecheck__ if super().__instancecheck__(instance): ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Users\alexw\coding\cpython\Lib\abc.py", line 119, in __instancecheck__ return _abc_instancecheck(cls, instance) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Users\alexw\coding\cpython\Lib\typing.py", line 1794, in __subclasscheck__ return super().__subclasscheck__(other) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 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 1897, in _proto_hook issubclass(other, Generic) and other._is_protocol): ^^^^^^^^^^^^^^^^^^AttributeError: type object 'Bar' has no attribute '_is_protocol'
Cc.@JelleZijlstra forPEP-695