bpo-44524: Don't modify MRO when inheriting from typing.Annotated (GH-27841)

Author: Fidget-Spinner

Lib/test/test_typing.py

@@ -4568,6 +4568,11 @@ def test_annotated_in_other_types(self):
  X = List[Annotated[T, 5]]
  self.assertEqual(X[int], List[Annotated[int, 5]])
 
+ def test_annotated_mro(self):
+ class X(Annotated[int, (1, 10)]): ...
+ self.assertEqual(X.__mro__, (X, int, object),
+ "Annotated should be transparent.")
+
 
 class TypeAliasTests(BaseTestCase):
  def test_canonical_usage_with_variable_annotation(self):

Lib/typing.py

@@ -1575,7 +1575,7 @@ def __init__(self, origin, metadata):
  if isinstance(origin, _AnnotatedAlias):
  metadata = origin.__metadata__ + metadata
  origin = origin.__origin__
- super().__init__(origin, origin, name="Annotated")
+ super().__init__(origin, origin)
  self.__metadata__ = metadata
 
  def copy_with(self, params):
@@ -1603,6 +1603,11 @@ def __eq__(self, other):
  def __hash__(self):
  return hash((self.__origin__, self.__metadata__))
 
+ def __getattr__(self, attr):
+ if attr in {'__name__', '__qualname__'}:
+ return 'Annotated'
+ return super().__getattr__(attr)
+
 
 class Annotated:
  """Add context specific metadata to a type.