gh-132493: Support deferred annotations in Protocols (#132494)

Author: JelleZijlstra

Lib/test/test_typing.py

@@ -4554,6 +4554,15 @@ class Commentable(Protocol):
         )
         self.assertIs(type(exc.__cause__), CustomError)
 
+    def test_deferred_evaluation_of_annotations(self):
+        class DeferredProto(Protocol):
+            x: DoesNotExist
+        self.assertEqual(get_protocol_members(DeferredProto), {"x"})
+        self.assertEqual(
+            annotationlib.get_annotations(DeferredProto, format=annotationlib.Format.STRING),
+            {'x': 'DoesNotExist'}
+        )
+
 
 class GenericTests(BaseTestCase):
 

Lib/typing.py

@@ -1801,7 +1801,9 @@ def _get_protocol_attrs(cls):
     for base in cls.__mro__[:-1]:  # without object
         if base.__name__ in {'Protocol', 'Generic'}:
             continue
-        annotations = getattr(base, '__annotations__', {})
+        annotations = _lazy_annotationlib.get_annotations(
+            base, format=_lazy_annotationlib.Format.FORWARDREF
+        )
         for attr in (*base.__dict__, *annotations):
             if not attr.startswith('_abc_') and attr not in EXCLUDED_ATTRIBUTES:
                 attrs.add(attr)

Misc/NEWS.d/next/Library/2025-04-13-21-35-50.gh-issue-132493.5SAQJn.rst

@@ -0,0 +1,2 @@
+Support creation of :class:`typing.Protocol` classes with annotations that
+cannot be resolved at class creation time.