gh-111874: Call __set_name__ on objects that define the method inside a typing.NamedTuple class dictionary as part of the creation of that class

Author: AlexWaygood

Lib/test/test_typing.py

@@ -7519,6 +7519,55 @@ class GenericNamedTuple(NamedTuple, Generic[T]):
 
         self.assertEqual(CallNamedTuple.__orig_bases__, (NamedTuple,))
 
+    def test_setname_called_on_non_members(self):
+        class Vanilla:
+            def __set_name__(self, owner, name):
+                self.name = name
+
+        class Foo(NamedTuple):
+            attr = Vanilla()
+
+        foo = Foo()
+        self.assertEqual(len(foo), 0)
+        self.assertNotIn('attr', Foo._fields)
+        self.assertIsInstance(foo.attr, Vanilla)
+        self.assertEqual(foo.attr.name, "attr")
+
+    def test_setname_raises_the_same_as_on_other_classes(self):
+        class CustomException(Exception): pass
+
+        class Annoying:
+            def __set_name__(self, owner, name):
+                raise CustomException("Cannot do that!")
+
+        with self.assertRaisesRegex(CustomException, "Cannot do that!") as cm:
+            class NormalClass:
+                attr = Annoying()
+        normal_exception = cm.exception
+
+        with self.assertRaisesRegex(CustomException, "Cannot do that!") as cm:
+            class NamedTupleClass:
+                attr = Annoying()
+        namedtuple_exception = cm.exception
+
+        self.assertIs(type(namedtuple_exception), CustomException)
+        self.assertIs(type(namedtuple_exception), type(normal_exception))
+
+        self.assertEqual(len(namedtuple_exception.__notes__), 1)
+        self.assertEqual(
+            len(namedtuple_exception.__notes__), len(normal_exception.__notes__)
+        )
+
+        expected_note = (
+            "Error calling __set_name__ on 'Annoying' instance "
+            "'attr' in 'NamedTupleClass'"
+        )
+        self.assertEqual(namedtuple_exception.__notes__[0], expected_note)
+        self.assertEqual(
+            namedtuple_exception.__notes__[0],
+            normal_exception.__notes__[0].replace("NormalClass", "NamedTupleClass")
+        )
+
 
 class TypedDictTests(BaseTestCase):
     def test_basics_functional_syntax(self):

Lib/typing.py

@@ -2726,11 +2726,20 @@ def __new__(cls, typename, bases, ns):
             class_getitem = _generic_class_getitem
             nm_tpl.__class_getitem__ = classmethod(class_getitem)
         # update from user namespace without overriding special namedtuple attributes
-        for key in ns:
+        for key, val in ns.items():
             if key in _prohibited:
                 raise AttributeError("Cannot overwrite NamedTuple attribute " + key)
             elif key not in _special and key not in nm_tpl._fields:
-                setattr(nm_tpl, key, ns[key])
+                setattr(nm_tpl, key, val)
+                if hasattr(type(val), "__set_name__"):
+                    try:
+                        type(val).__set_name__(val, nm_tpl, key)
+                    except Exception as e:
+                        e.add_note(
+                            f"Error calling __set_name__ on {type(val).__name__!r} "
+                            f"instance {key!r} in {typename!r}"
+                        )
+                        raise
         if Generic in bases:
             nm_tpl.__init_subclass__()
         return nm_tpl

Misc/NEWS.d/next/Library/2023-11-09-11-07-34.gh-issue-111874.dzYc3j.rst

@@ -0,0 +1,4 @@
+When creating a :class:`typing.NamedTuple` class, ensure
+:func:`__set_name__` is called on all objects that define ``__set_name__``
+and exist in the values of the ``NamedTuple`` class's class dictionary.
+Patch by Alex Waygood.