pythongh-146553: Fix infinite loop in typing.get_type_hints() on circular __wrapped__

python#146553

Author: raminfp

Lib/test/test_typing.py

@@ -6837,6 +6837,34 @@ def test_get_type_hints_wrapped_decoratored_func(self):
         self.assertEqual(gth(ForRefExample.func), expects)
         self.assertEqual(gth(ForRefExample.nested), expects)
 
+    def test_get_type_hints_wrapped_cycle_self(self):
+        # gh-146553: __wrapped__ self-reference must raise ValueError,
+        # not loop forever.
+        def f(x: int) -> str: ...
+        f.__wrapped__ = f
+        with self.assertRaises(ValueError):
+            get_type_hints(f)
+
+    def test_get_type_hints_wrapped_cycle_mutual(self):
+        # gh-146553: mutual __wrapped__ cycle (a -> b -> a) must raise
+        # ValueError, not loop forever.
+        def a(): ...
+        def b(): ...
+        a.__wrapped__ = b
+        b.__wrapped__ = a
+        with self.assertRaises(ValueError):
+            get_type_hints(a)
+
+    def test_get_type_hints_wrapped_chain_no_cycle(self):
+        # gh-146553: a valid (non-cyclic) __wrapped__ chain must still work.
+        def inner(x: int) -> str: ...
+        def middle(x: int) -> str: ...
+        middle.__wrapped__ = inner
+        def outer(x: int) -> str: ...
+        outer.__wrapped__ = middle
+        # No cycle — should return the annotations without raising.
+        self.assertEqual(get_type_hints(outer), {'x': int, 'return': str})
+
     def test_get_type_hints_annotated(self):
         def foobar(x: List['X']): ...
         X = Annotated[int, (1, 10)]

Lib/typing.py

@@ -2485,8 +2485,18 @@ def get_type_hints(obj, globalns=None, localns=None, include_extras=False,
         else:
             nsobj = obj
             # Find globalns for the unwrapped object.
+            # Use an id-based visited set to detect and break on cycles in the
+            # __wrapped__ chain (e.g. f.__wrapped__ = f), matching the behavior
+            # of inspect.unwrap().
+            _seen_ids = {id(nsobj)}
             while hasattr(nsobj, '__wrapped__'):
                 nsobj = nsobj.__wrapped__
+                _nsobj_id = id(nsobj)
+                if _nsobj_id in _seen_ids:
+                    raise ValueError(
+                        f'wrapper loop when unwrapping {obj!r}'
+                    )
+                _seen_ids.add(_nsobj_id)
             globalns = getattr(nsobj, '__globals__', {})
         if localns is None:
             localns = globalns

Misc/NEWS.d/next/Library/2026-03-28-11-43-25.gh-issue-146553.mXaWza.rst

@@ -0,0 +1,4 @@
+Fix :func:`typing.get_type_hints` hanging indefinitely when a callable has a
+circular ``__wrapped__`` chain (e.g. ``f.__wrapped__ = f``). A
+:exc:`ValueError` is now raised on cycle detection, matching the behavior of
+:func:`inspect.unwrap`.