gh-104797: Allow Protocols to inherit from collections.abc.Buffer (#104827)

Author: JelleZijlstra

Lib/test/test_typing.py

@@ -3546,6 +3546,22 @@ def close(self):
         self.assertIsSubclass(B, Custom)
         self.assertNotIsSubclass(A, Custom)
 
+        @runtime_checkable
+        class ReleasableBuffer(collections.abc.Buffer, Protocol):
+            def __release_buffer__(self, mv: memoryview) -> None: ...
+
+        class C: pass
+        class D:
+            def __buffer__(self, flags: int) -> memoryview:
+                return memoryview(b'')
+            def __release_buffer__(self, mv: memoryview) -> None:
+                pass
+
+        self.assertIsSubclass(D, ReleasableBuffer)
+        self.assertIsInstance(D(), ReleasableBuffer)
+        self.assertNotIsSubclass(C, ReleasableBuffer)
+        self.assertNotIsInstance(C(), ReleasableBuffer)
+
     def test_builtin_protocol_allowlist(self):
         with self.assertRaises(TypeError):
             class CustomProtocol(TestCase, Protocol):

Lib/typing.py

@@ -1740,7 +1740,7 @@ def _allow_reckless_class_checks(depth=3):
 _PROTO_ALLOWLIST = {
     'collections.abc': [
         'Callable', 'Awaitable', 'Iterable', 'Iterator', 'AsyncIterable',
-        'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',
+        'Hashable', 'Sized', 'Container', 'Collection', 'Reversible', 'Buffer',
     ],
     'contextlib': ['AbstractContextManager', 'AbstractAsyncContextManager'],
 }

Misc/NEWS.d/next/Library/2023-05-23-17-43-52.gh-issue-104797.NR7KzF.rst

@@ -0,0 +1,2 @@
+Allow :class:`typing.Protocol` classes to inherit from
+:class:`collections.abc.Buffer`. Patch by Jelle Zijlstra.