python · srittau · May 24, 2023 · May 24, 2023 · May 24, 2023
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,3 +1,9 @@
+# Unreleased
+
+- Fix regression in version 4.6.1 where comparing a generic class against a 
+  runtime-checkable protocol using `isinstance()` would cause `AttributeError`
+  to be raised if using Python 3.7
+
 # Release 4.6.1 (May 23, 2023)

 - Change deprecated `@runtime` to formal API `@runtime_checkable` in the error

diff --git a/src/test_typing_extensions.py b/src/test_typing_extensions.py
@@ -2246,6 +2246,28 @@ class Foo: ...
        del f.x
        self.assertNotIsInstance(f, HasX)

+    def test_protocols_isinstance_generic_classes(self):
+        T = TypeVar("T")
+
+        class Foo(Generic[T]):
+            x: T
+
+            def __init__(self, x):
+                self.x = x
+
+        class Bar(Foo[int]):
+            ...
+
+        @runtime_checkable
+        class HasX(Protocol):
+            x: int
+
+        foo = Foo(1)
+        self.assertIsInstance(foo, HasX)
+
+        bar = Bar(2)
+        self.assertIsInstance(bar, HasX)
+
    def test_protocols_support_register(self):
        @runtime_checkable
        class P(Protocol):
@@ -4330,6 +4352,7 @@ class Y(Generic[T], NamedTuple):

                a = A(3)
                self.assertIs(type(a), G)
+                self.assertIsInstance(a, G)
                self.assertEqual(a.x, 3)

                things = "arguments" if sys.version_info >= (3, 11) else "parameters"

diff --git a/src/typing_extensions.py b/src/typing_extensions.py
@@ -9,7 +9,6 @@
 import typing
 import warnings

-
 __all__ = [
    # Super-special typing primitives.
    'Any',
@@ -659,7 +658,9 @@ def _proto_hook(cls, other):
                    isinstance(annotations, collections.abc.Mapping)
                    and attr in annotations
                    and issubclass(other, (typing.Generic, _ProtocolMeta))
-                    and other._is_protocol
+                    # All subclasses of Generic have an _is_proto attribute on 3.8+
+                    # But not on 3.7
+                    and getattr(other, "_is_protocol", False)
                ):
                    break
            else: