gh-107576: Ensure `__orig_bases__` are our own in `get_original_bases` (#107584)

Co-authored-by: Chris Bouchard <chris@upliftinglemma.net>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Lib/test/test_types.py

@@ -1397,6 +1397,7 @@ class ClassCreationTests(unittest.TestCase):
         class B(typing.Generic[T]): pass
         class C(B[int]): pass
         class D(B[str], float): pass
+
         self.assertEqual(types.get_original_bases(A), (object,))
         self.assertEqual(types.get_original_bases(B), (typing.Generic[T],))
         self.assertEqual(types.get_original_bases(C), (B[int],))
@@ -1409,6 +1410,18 @@ class ClassCreationTests(unittest.TestCase):
         self.assertEqual(types.get_original_bases(E), (list[T],))
         self.assertEqual(types.get_original_bases(F), (list[int],))
 
+        class FirstBase(typing.Generic[T]): pass
+        class SecondBase(typing.Generic[T]): pass
+        class First(FirstBase[int]): pass
+        class Second(SecondBase[int]): pass
+        class G(First, Second): pass
+        self.assertEqual(types.get_original_bases(G), (First, Second))
+
+        class First_(typing.Generic[T]): pass
+        class Second_(typing.Generic[T]): pass
+        class H(First_, Second_): pass
+        self.assertEqual(types.get_original_bases(H), (First_, Second_))
+
         class ClassBasedNamedTuple(typing.NamedTuple):
             x: int
 

Lib/types.py

@@ -165,14 +165,11 @@ def get_original_bases(cls, /):
         assert get_original_bases(int) == (object,)
     """
     try:
-        return cls.__orig_bases__
+        return cls.__dict__.get("__orig_bases__", cls.__bases__)
     except AttributeError:
-        try:
-            return cls.__bases__
-        except AttributeError:
-            raise TypeError(
-                f'Expected an instance of type, not {type(cls).__name__!r}'
-            ) from None
+        raise TypeError(
+            f"Expected an instance of type, not {type(cls).__name__!r}"
+        ) from None
 
 
 class DynamicClassAttribute:

Misc/NEWS.d/next/Library/2023-08-03-11-31-11.gh-issue-107576.pO_s9I.rst

@@ -0,0 +1,3 @@
+Fix :func:`types.get_original_bases` to only return
+:attr:`!__orig_bases__` if it is present on ``cls`` directly. Patch by
+James Hilton-Balfe.