python · JelleZijlstra · Apr 6, 2025 · Apr 6, 2025
diff --git a/Lib/test/test_warnings/__init__.py b/Lib/test/test_warnings/__init__.py
@@ -1628,6 +1628,25 @@ class Child(Base, Mixin):
         instance = Child(42)
         self.assertEqual(instance.a, 42)
 
+    def test_do_not_shadow_user_arguments(self):
+        new_called = False
+        new_called_cls = None
+
+        @deprecated("MyMeta will go away soon")
+        class MyMeta(type):
+            def __new__(mcs, name, bases, attrs, cls=None):
+                nonlocal new_called, new_called_cls
+                new_called = True
+                new_called_cls = cls
+                return super().__new__(mcs, name, bases, attrs)
+
+        with self.assertWarnsRegex(DeprecationWarning, "MyMeta will go away soon"):
+            class Foo(metaclass=MyMeta, cls='haha'):
+                pass
+
+        self.assertTrue(new_called)
+        self.assertEqual(new_called_cls, 'haha')
+
     def test_existing_init_subclass(self):
         @deprecated("C will go away soon")
         class C:

diff --git a/Lib/warnings.py b/Lib/warnings.py
@@ -589,7 +589,7 @@ def __call__(self, arg, /):
             original_new = arg.__new__
 
             @functools.wraps(original_new)
-            def __new__(cls, *args, **kwargs):
+            def __new__(cls, /, *args, **kwargs):
                 if cls is arg:
                     warn(msg, category=category, stacklevel=stacklevel + 1)
                 if original_new is not object.__new__:

diff --git a/Misc/NEWS.d/next/Library/2025-04-06-16-12-49.gh-issue-132159.WvBfBm.rst b/Misc/NEWS.d/next/Library/2025-04-06-16-12-49.gh-issue-132159.WvBfBm.rst
@@ -0,0 +1 @@
+Do not shadow user arguments in generated :meth:`!__new__` by decorator :class:`warnings.deprecated`. Patch by Xuehai Pan.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Do not shadow user arguments in generated :meth:`!__new__` by decorator :class:`warnings.deprecated`. Patch by Xuehai Pan.