From cbea6f83873647f8149021732f6c4af67ea03efc Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 18:33:26 -0400
Subject: [PATCH 01/20] Introduce NoExtraItems as a C-level singleton

Implemented _Py_NoExtraItemsStruct and _Py_NoExtraItemsStruct
---
 Objects/typevarobject.c | 54 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index cead6e69af5451..403ac547546489 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -123,6 +123,60 @@ PyTypeObject _PyNoDefault_Type = {
 
 PyObject _Py_NoDefaultStruct = _PyObject_HEAD_INIT(&_PyNoDefault_Type);
 
+/* NoExtraItems: a marker object for TypeDict extra-items when it's unset. */
+
+static PyObject *
+NoExtraItems_repr(PyObject *op)
+{
+    return PyUnicode_FromString("typing.NoExtraItems");
+}
+
+static PyObject *
+NoExtraItems_reduce(PyObject *op, PyObject *Py_UNUSED(ignored))
+{
+    return PyUnicode_FromString("NoExtraItems");
+}
+
+static PyMethodDef noextraitems_methods[] = {
+    {"__reduce__", NoExtraItems_reduce, METH_NOARGS, NULL},
+    {NULL, NULL}
+};
+
+static PyObject *
+noextraitems_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
+{
+    if (PyTuple_GET_SIZE(args) || (kwargs && PyDict_GET_SIZE(kwargs))) {
+        PyErr_SetString(PyExc_TypeError, "NoExtraItemsType takes no arguments");
+        return NULL;
+    }
+    return (PyObject *)&_Py_NoExtraItemsStruct;
+}
+
+static void
+noextraitems_dealloc(PyObject *obj)
+{
+    /* Immortal singleton: never actually deallocates. */
+    _Py_SetImmortal(obj);
+}
+
+PyDoc_STRVAR(noextraitems_doc,
+"NoExtraItemsType()\n"
+"--\n\n"
+"The type of the NoExtraItems singleton.");
+
+PyTypeObject _PyNoExtraItems_Type = {
+    PyVarObject_HEAD_INIT(&PyType_Type, 0)
+    "NoExtraItemsType",
+    .tp_dealloc = noextraitems_dealloc,
+    .tp_repr = NoExtraItems_repr,
+    .tp_flags = Py_TPFLAGS_DEFAULT,
+    .tp_doc = noextraitems_doc,
+    .tp_methods = noextraitems_methods,
+    .tp_new = noextraitems_new,
+};
+
+PyObject _Py_NoExtraItemsStruct = _PyObject_HEAD_INIT(&_PyNoExtraItems_Type);
+
 typedef struct {
     PyObject_HEAD
     PyObject *value;

From 4cde2f923cd58035710cd6ee06c19f2103555e35 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 18:47:52 -0400
Subject: [PATCH 02/20] expose NoExtraItems via _typing

---
 Include/internal/pycore_typevarobject.h | 2 ++
 Modules/_typingmodule.c                 | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/Include/internal/pycore_typevarobject.h b/Include/internal/pycore_typevarobject.h
index 4d7556e68cdaee..255b716846f535 100644
--- a/Include/internal/pycore_typevarobject.h
+++ b/Include/internal/pycore_typevarobject.h
@@ -21,6 +21,8 @@ extern int _Py_typing_type_repr(PyUnicodeWriter *, PyObject *);
 extern PyTypeObject _PyTypeAlias_Type;
 extern PyTypeObject _PyNoDefault_Type;
 extern PyObject _Py_NoDefaultStruct;
+extern PyTypeObject _PyNoExtraItems_Type;
+extern PyObject _Py_NoExtraItemsStruct;
 
 #ifdef __cplusplus
 }
diff --git a/Modules/_typingmodule.c b/Modules/_typingmodule.c
index e51279c808a2e1..89d2a956eeb721 100644
--- a/Modules/_typingmodule.c
+++ b/Modules/_typingmodule.c
@@ -70,6 +70,9 @@ _typing_exec(PyObject *m)
     if (PyModule_AddObjectRef(m, "NoDefault", (PyObject *)&_Py_NoDefaultStruct) < 0) {
         return -1;
     }
+    if (PyModule_AddObjectRef(m, "NoExtraItems", (PyObject *)&_Py_NoExtraItemsStruct) < 0) {
+        return -1;
+    }
     return 0;
 }
 

From 06de7a94006a33569ddaf9274368a2c925b5bf32 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 19:02:38 -0400
Subject: [PATCH 03/20] Clearer comments in the C internals

---
 Objects/typevarobject.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index 403ac547546489..a09c005ac0667f 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -123,7 +123,7 @@ PyTypeObject _PyNoDefault_Type = {
 
 PyObject _Py_NoDefaultStruct = _PyObject_HEAD_INIT(&_PyNoDefault_Type);
 
-/* NoExtraItems: a marker object for TypeDict extra-items when it's unset. */
+/* NoExtraItems: a marker object for TypeDict extra_items when it's unset. */
 
 static PyObject *
 NoExtraItems_repr(PyObject *op)
@@ -155,7 +155,10 @@ noextraitems_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
 static void
 noextraitems_dealloc(PyObject *obj)
 {
-    /* Immortal singleton: never actually deallocates. */
+    /* This should never get called, but we also don't want to SEGV if
+     * we accidentally decref NoDefault out of existence. Instead,
+     * since NoDefault is an immortal object, re-set the reference count.
+     */
     _Py_SetImmortal(obj);
 }
 

From 407bf7488d83ac5bd60541dc6230990c1d50d2ab Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 19:08:34 -0400
Subject: [PATCH 04/20] Import NoExtraItems into typing

---
 Lib/typing.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Lib/typing.py b/Lib/typing.py
index 8c1d265019bb94..19b0a528c0252f 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -40,6 +40,7 @@
     Generic,
     Union,
     NoDefault,
+    NoExtraItems,
 )
 
 # Please keep __all__ alphabetized within each category.
@@ -141,6 +142,7 @@
     'no_type_check',
     'no_type_check_decorator',
     'NoDefault',
+    'NoExtraItems',
     'NoReturn',
     'NotRequired',
     'overload',

From f9755d3e05f54478f323cf88ae941e4d9391d56f Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 19:18:55 -0400
Subject: [PATCH 05/20] Update _TypedDictMeta and TypedDict

They now both accept `closed` and `extra_items` as parameters.
For introspection, these arguments are also mapped to 2 new attributes:
`__closed__` and `__extra_items__`.
---
 Lib/typing.py | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index 19b0a528c0252f..441a64dfb0ad2e 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3080,7 +3080,8 @@ def _get_typeddict_qualifiers(annotation_type):
 
 
 class _TypedDictMeta(type):
-    def __new__(cls, name, bases, ns, total=True):
+    def __new__(cls, name, bases, ns, total=True, closed=None,
+                extra_items=NoExtraItems):
         """Create a new typed dict class object.
 
         This method is called when TypedDict is subclassed,
@@ -3092,6 +3093,8 @@ def __new__(cls, name, bases, ns, total=True):
             if type(base) is not _TypedDictMeta and base is not Generic:
                 raise TypeError('cannot inherit from both a TypedDict type '
                                 'and a non-TypedDict base class')
+        if closed is not None and extra_items is not NoExtraItems:
+            raise TypeError(f"Cannot combine closed={closed!r} and extra_items")
 
         if any(issubclass(b, Generic) for b in bases):
             generic_base = (Generic,)
@@ -3203,6 +3206,8 @@ def __annotate__(format):
         tp_dict.__readonly_keys__ = frozenset(readonly_keys)
         tp_dict.__mutable_keys__ = frozenset(mutable_keys)
         tp_dict.__total__ = total
+        tp_dict.__closed__ = closed
+        tp_dict.__extra_items__ = extra_items
         return tp_dict
 
     __call__ = dict  # static method
@@ -3214,7 +3219,8 @@ def __subclasscheck__(cls, other):
     __instancecheck__ = __subclasscheck__
 
 
-def TypedDict(typename, fields, /, *, total=True):
+def TypedDict(typename, fields, /, *, total=True, closed=None,
+              extra_items=NoExtraItems):
     """A simple typed namespace. At runtime it is equivalent to a plain dict.
 
     TypedDict creates a dictionary type such that a type checker will expect all
@@ -3275,7 +3281,8 @@ class DatabaseUser(TypedDict):
         # Setting correct module is necessary to make typed dict classes pickleable.
         ns['__module__'] = module
 
-    td = _TypedDictMeta(typename, (), ns, total=total)
+    td = _TypedDictMeta(typename, (), ns, total=total, closed=closed,
+                        extra_items=extra_items)
     td.__orig_bases__ = (TypedDict,)
     return td
 

From 385812a5294956baba3cb653f9b1f0f22b08fb96 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 19:37:32 -0400
Subject: [PATCH 06/20] fix typo

---
 Objects/typevarobject.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index a09c005ac0667f..540811000dd9be 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -156,7 +156,7 @@ static void
 noextraitems_dealloc(PyObject *obj)
 {
     /* This should never get called, but we also don't want to SEGV if
-     * we accidentally decref NoDefault out of existence. Instead,
+     * we accidentally decref NoExtraItems out of existence. Instead,
      * since NoDefault is an immortal object, re-set the reference count.
      */
     _Py_SetImmortal(obj);

From bdbae49abca5b645007edce6aca500a292bf2ffc Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 19:57:55 -0400
Subject: [PATCH 07/20] Port over the relevant tests

---
 Lib/test/test_typing.py | 99 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 98 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 6317d4657619f0..8c6cc2c08b68dc 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -41,7 +41,7 @@
 from typing import Self, LiteralString
 from typing import TypeAlias
 from typing import ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs
-from typing import TypeGuard, TypeIs, NoDefault
+from typing import TypeGuard, TypeIs, NoDefault, NoExtraItems
 import abc
 import textwrap
 import typing
@@ -8770,6 +8770,32 @@ class ChildWithInlineAndOptional(Untotal, Inline):
                     class Wrong(*bases):
                         pass
 
+    def test_closed_values(self):
+        class Implicit(TypedDict): ...
+        class ExplicitTrue(TypedDict, closed=True): ...
+        class ExplicitFalse(TypedDict, closed=False): ...
+
+        self.assertIsNone(Implicit.__closed__)
+        self.assertIs(ExplicitTrue.__closed__, True)
+        self.assertIs(ExplicitFalse.__closed__, False)
+
+    def test_extra_items_class_arg(self):
+        class TD(TypedDict, extra_items=int):
+            a: str
+
+        self.assertIs(TD.__extra_items__, int)
+        self.assertEqual(TD.__annotations__, {'a': str})
+        self.assertEqual(TD.__required_keys__, frozenset({'a'}))
+        self.assertEqual(TD.__optional_keys__, frozenset())
+
+        class NoExtra(TypedDict):
+            a: str
+
+        self.assertIs(NoExtra.__extra_items__, NoExtraItems)
+        self.assertEqual(NoExtra.__annotations__, {'a': str})
+        self.assertEqual(NoExtra.__required_keys__, frozenset({'a'}))
+        self.assertEqual(NoExtra.__optional_keys__, frozenset())
+
     def test_is_typeddict(self):
         self.assertIs(is_typeddict(Point2D), True)
         self.assertIs(is_typeddict(Union[str, int]), False)
@@ -9097,6 +9123,71 @@ class AllTheThings(TypedDict):
             },
         )
 
+    def test_closed_inheritance(self):
+        class Base(TypedDict, extra_items=ReadOnly[Union[str, None]]):
+            a: int
+
+        self.assertEqual(Base.__required_keys__, frozenset({"a"}))
+        self.assertEqual(Base.__optional_keys__, frozenset({}))
+        self.assertEqual(Base.__readonly_keys__, frozenset({}))
+        self.assertEqual(Base.__mutable_keys__, frozenset({"a"}))
+        self.assertEqual(Base.__annotations__, {"a": int})
+        self.assertEqual(Base.__extra_items__, ReadOnly[Union[str, None]])
+        self.assertIsNone(Base.__closed__)
+
+        class Child(Base, extra_items=int):
+            a: str
+
+        self.assertEqual(Child.__required_keys__, frozenset({'a'}))
+        self.assertEqual(Child.__optional_keys__, frozenset({}))
+        self.assertEqual(Child.__readonly_keys__, frozenset({}))
+        self.assertEqual(Child.__mutable_keys__, frozenset({'a'}))
+        self.assertEqual(Child.__annotations__, {"a": str})
+        self.assertIs(Child.__extra_items__, int)
+        self.assertIsNone(Child.__closed__)
+
+        class GrandChild(Child, closed=True):
+            a: float
+
+        self.assertEqual(GrandChild.__required_keys__, frozenset({'a'}))
+        self.assertEqual(GrandChild.__optional_keys__, frozenset({}))
+        self.assertEqual(GrandChild.__readonly_keys__, frozenset({}))
+        self.assertEqual(GrandChild.__mutable_keys__, frozenset({'a'}))
+        self.assertEqual(GrandChild.__annotations__, {"a": float})
+        self.assertIs(GrandChild.__extra_items__, NoExtraItems)
+        self.assertIs(GrandChild.__closed__, True)
+
+        class GrandGrandChild(GrandChild):
+            ...
+        self.assertEqual(GrandGrandChild.__required_keys__, frozenset({'a'}))
+        self.assertEqual(GrandGrandChild.__optional_keys__, frozenset({}))
+        self.assertEqual(GrandGrandChild.__readonly_keys__, frozenset({}))
+        self.assertEqual(GrandGrandChild.__mutable_keys__, frozenset({'a'}))
+        self.assertEqual(GrandGrandChild.__annotations__, {"a": float})
+        self.assertIs(GrandGrandChild.__extra_items__, NoExtraItems)
+        self.assertIsNone(GrandGrandChild.__closed__)
+
+    def test_implicit_extra_items(self):
+        class Base(TypedDict):
+            a: int
+
+        self.assertIs(Base.__extra_items__, NoExtraItems)
+        self.assertIsNone(Base.__closed__)
+
+        class ChildA(Base, closed=True):
+            ...
+
+        self.assertEqual(ChildA.__extra_items__, NoExtraItems)
+        self.assertIs(ChildA.__closed__, True)
+
+    def test_cannot_combine_closed_and_extra_items(self):
+        with self.assertRaisesRegex(
+            TypeError,
+            "Cannot combine closed=True and extra_items"
+        ):
+            class TD(TypedDict, closed=True, extra_items=range):
+                x: str
+
     def test_annotations(self):
         # _type_check is applied
         with self.assertRaisesRegex(TypeError, "Plain typing.Final is not valid as type argument"):
@@ -9326,6 +9417,12 @@ class A(typing.Match):
             class B(typing.Pattern):
                 pass
 
+    def test_typed_dict_signature(self):
+        self.assertListEqual(
+            list(inspect.signature(TypedDict).parameters),
+            ['typename', 'fields', 'total', 'closed', 'extra_items']
+        )
+
 
 class AnnotatedTests(BaseTestCase):
 

From e68c2edf9630855f73c7a781b96e8510f93f246f Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Sun, 17 Aug 2025 23:23:09 -0400
Subject: [PATCH 08/20] Updated docstring and error messages

---
 Lib/typing.py | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index 441a64dfb0ad2e..b68db337e28e4f 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3091,10 +3091,10 @@ def __new__(cls, name, bases, ns, total=True, closed=None,
         """
         for base in bases:
             if type(base) is not _TypedDictMeta and base is not Generic:
-                raise TypeError('cannot inherit from both a TypedDict type '
+                raise TypeError('Cannot inherit from both a TypedDict type '
                                 'and a non-TypedDict base class')
         if closed is not None and extra_items is not NoExtraItems:
-            raise TypeError(f"Cannot combine closed={closed!r} and extra_items")
+            raise TypeError(f"Cannot use both closed and extra_items")
 
         if any(issubclass(b, Generic) for b in bases):
             generic_base = (Generic,)
@@ -3274,6 +3274,26 @@ class DatabaseUser(TypedDict):
             id: ReadOnly[int]  # the "id" key must not be modified
             username: str      # the "username" key can be changed
 
+    The *closed* argument controls whether the TypedDict allows additional
+    non-required items during inheritance and assignability checks.
+    If closed=True, the TypedDict is closed to additional items::
+
+        Point2D = TypedDict('Point2D', {'x': int, 'y': int}, closed=True)
+        class Point3D(Point2D):
+            z: int  # Type checker error
+
+    Passing closed=False explicitly requests TypedDict's default open behavior.
+    If closed is not provided, the behavior is inherited from the superclass.
+
+    The *extra_items* argument can instead be used to specify the type of
+    additional non-required keys::
+
+        Point2D = TypedDict('Point2D', {'x': int, 'y': int}, extra_items=int)
+        class Point3D(Point2D):
+            z: int      # OK
+            label: str  # Type checker error
+
+    See PEP 728 for more information about closed and extra_items.
     """
     ns = {'__annotations__': dict(fields)}
     module = _caller()

From 8203bc19104b10842008b848da3332f7279cacfc Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 18 Aug 2025 07:11:57 -0400
Subject: [PATCH 09/20] NEWS entry

---
 .../Library/2025-08-18-07-10-55.gh-issue-137840.9b7AnG.rst     | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2025-08-18-07-10-55.gh-issue-137840.9b7AnG.rst

diff --git a/Misc/NEWS.d/next/Library/2025-08-18-07-10-55.gh-issue-137840.9b7AnG.rst b/Misc/NEWS.d/next/Library/2025-08-18-07-10-55.gh-issue-137840.9b7AnG.rst
new file mode 100644
index 00000000000000..5ea25a86204318
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-08-18-07-10-55.gh-issue-137840.9b7AnG.rst
@@ -0,0 +1,3 @@
+:class:`typing.TypedDict` now supports the ``closed`` and ``extra_items``
+keyword arguments (as described in :pep:`728`) to control whether additional
+non-required keys are allowed and to specify their value type.

From 1b3ce5258fdd217ba9f56939c77210a8fc3f0a0c Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 18 Aug 2025 22:44:35 -0400
Subject: [PATCH 10/20] New draft of docstring and error message

---
 Lib/typing.py | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index b68db337e28e4f..d7150d09017352 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3094,7 +3094,7 @@ def __new__(cls, name, bases, ns, total=True, closed=None,
                 raise TypeError('Cannot inherit from both a TypedDict type '
                                 'and a non-TypedDict base class')
         if closed is not None and extra_items is not NoExtraItems:
-            raise TypeError(f"Cannot use both closed and extra_items")
+            raise TypeError(f"Closed cannot be specified with extra_items")
 
         if any(issubclass(b, Generic) for b in bases):
             generic_base = (Generic,)
@@ -3274,7 +3274,7 @@ class DatabaseUser(TypedDict):
             id: ReadOnly[int]  # the "id" key must not be modified
             username: str      # the "username" key can be changed
 
-    The *closed* argument controls whether the TypedDict allows additional
+    The closed argument controls whether the TypedDict allows additional
     non-required items during inheritance and assignability checks.
     If closed=True, the TypedDict is closed to additional items::
 
@@ -3284,15 +3284,21 @@ class Point3D(Point2D):
 
     Passing closed=False explicitly requests TypedDict's default open behavior.
     If closed is not provided, the behavior is inherited from the superclass.
+    A type checker is only expected to support a literal False or True as the
+    value of the closed argument.
 
-    The *extra_items* argument can instead be used to specify the type of
-    additional non-required keys::
+    The extra_items argument can instead be used to specify the assignable type
+    of unknown non-required keys::
 
         Point2D = TypedDict('Point2D', {'x': int, 'y': int}, extra_items=int)
         class Point3D(Point2D):
             z: int      # OK
             label: str  # Type checker error
 
+    The extra_items argument is also inherited through subclassing. It is unset
+    by default, and it may not be used with the closed argument at the same
+    time.
+
     See PEP 728 for more information about closed and extra_items.
     """
     ns = {'__annotations__': dict(fields)}

From 2f5c42e37fd5fd4f6ce4f43f402ce6535bf8eef2 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 18 Aug 2025 22:49:10 -0400
Subject: [PATCH 11/20] just use the original error message

---
 Lib/typing.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index d7150d09017352..1a7c0e6eef295e 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3094,7 +3094,7 @@ def __new__(cls, name, bases, ns, total=True, closed=None,
                 raise TypeError('Cannot inherit from both a TypedDict type '
                                 'and a non-TypedDict base class')
         if closed is not None and extra_items is not NoExtraItems:
-            raise TypeError(f"Closed cannot be specified with extra_items")
+            raise TypeError(f"Cannot combine closed={closed!r} and extra_items")
 
         if any(issubclass(b, Generic) for b in bases):
             generic_base = (Generic,)

From 1bd3a6d3d88a87f6707ba71f2ed3cb6af443c587 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 18 Aug 2025 23:25:10 -0400
Subject: [PATCH 12/20] fix typo

---
 Objects/typevarobject.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index 540811000dd9be..66f0b5575baf64 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -123,7 +123,7 @@ PyTypeObject _PyNoDefault_Type = {
 
 PyObject _Py_NoDefaultStruct = _PyObject_HEAD_INIT(&_PyNoDefault_Type);
 
-/* NoExtraItems: a marker object for TypeDict extra_items when it's unset. */
+/* NoExtraItems: a marker object for TypeDict extra_items when its unset. */
 
 static PyObject *
 NoExtraItems_repr(PyObject *op)
@@ -157,7 +157,7 @@ noextraitems_dealloc(PyObject *obj)
 {
     /* This should never get called, but we also don't want to SEGV if
      * we accidentally decref NoExtraItems out of existence. Instead,
-     * since NoDefault is an immortal object, re-set the reference count.
+     * since NoExtraItems is an immortal object, re-set the reference count.
      */
     _Py_SetImmortal(obj);
 }

From 42a1aac75927dde9911867a0d0da23b6ebf1c77e Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 18 Aug 2025 23:35:22 -0400
Subject: [PATCH 13/20] undo capitalization

---
 Lib/typing.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index 1a7c0e6eef295e..7c45563be720a3 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3091,7 +3091,7 @@ def __new__(cls, name, bases, ns, total=True, closed=None,
         """
         for base in bases:
             if type(base) is not _TypedDictMeta and base is not Generic:
-                raise TypeError('Cannot inherit from both a TypedDict type '
+                raise TypeError('cannot inherit from both a TypedDict type '
                                 'and a non-TypedDict base class')
         if closed is not None and extra_items is not NoExtraItems:
             raise TypeError(f"Cannot combine closed={closed!r} and extra_items")

From 36ee4d2f4594087dbf3bc8ae6a1acb7a0e1ea768 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Tue, 19 Aug 2025 00:47:21 -0400
Subject: [PATCH 14/20] fix typo x2

---
 Objects/typevarobject.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index 66f0b5575baf64..bb13fa9513afe6 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -123,7 +123,7 @@ PyTypeObject _PyNoDefault_Type = {
 
 PyObject _Py_NoDefaultStruct = _PyObject_HEAD_INIT(&_PyNoDefault_Type);
 
-/* NoExtraItems: a marker object for TypeDict extra_items when its unset. */
+/* NoExtraItems: a marker object for TypeDict extra_items when it's unset. */
 
 static PyObject *
 NoExtraItems_repr(PyObject *op)

From 503b82584f1c73bd7aea45906c549b03f72b6140 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Tue, 19 Aug 2025 23:52:02 -0400
Subject: [PATCH 15/20] fix typo x3

---
 Objects/typevarobject.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index bb13fa9513afe6..8ffa00c332dddb 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -123,7 +123,7 @@ PyTypeObject _PyNoDefault_Type = {
 
 PyObject _Py_NoDefaultStruct = _PyObject_HEAD_INIT(&_PyNoDefault_Type);
 
-/* NoExtraItems: a marker object for TypeDict extra_items when it's unset. */
+/* NoExtraItems: a marker object for TypedDict extra_items when it's unset. */
 
 static PyObject *
 NoExtraItems_repr(PyObject *op)

From 1f23caa67a2b8309123062af8e55d819edd0c470 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Wed, 20 Aug 2025 00:49:41 -0400
Subject: [PATCH 16/20] Hush the c-analyzer: NoExtraItems is a singleton

---
 Tools/c-analyzer/cpython/ignored.tsv | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Tools/c-analyzer/cpython/ignored.tsv b/Tools/c-analyzer/cpython/ignored.tsv
index 4fdb7b3cd1abf2..f686a1f9a9a380 100644
--- a/Tools/c-analyzer/cpython/ignored.tsv
+++ b/Tools/c-analyzer/cpython/ignored.tsv
@@ -344,6 +344,8 @@ Objects/obmalloc.c	-	obmalloc_state_main	-
 Objects/obmalloc.c	-	obmalloc_state_initialized	-
 Objects/typeobject.c	-	name_op	-
 Objects/typeobject.c	-	slotdefs	-
+Objects/typevarobject.c	-	_PyNoExtraItems_Type	-
+Objects/typevarobject.c	-	_Py_NoExtraItemsStruct	-
 Objects/unicodeobject.c	-	stripfuncnames	-
 Objects/unicodeobject.c	-	utf7_category	-
 Objects/unicodeobject.c	unicode_decode_call_errorhandler_wchar	argparse	-

From 9a9c5c59a2bbd202fb8bb86b6e406affe49124d5 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 25 Aug 2025 21:21:17 -0400
Subject: [PATCH 17/20] remove c-level NoExtraItems singleton

---
 Include/internal/pycore_typevarobject.h |  2 -
 Lib/test/test_typing.py                 |  2 +-
 Lib/typing.py                           |  1 -
 Modules/_typingmodule.c                 |  3 --
 Objects/typevarobject.c                 | 57 -------------------------
 Tools/c-analyzer/cpython/ignored.tsv    |  2 -
 6 files changed, 1 insertion(+), 66 deletions(-)

diff --git a/Include/internal/pycore_typevarobject.h b/Include/internal/pycore_typevarobject.h
index 255b716846f535..4d7556e68cdaee 100644
--- a/Include/internal/pycore_typevarobject.h
+++ b/Include/internal/pycore_typevarobject.h
@@ -21,8 +21,6 @@ extern int _Py_typing_type_repr(PyUnicodeWriter *, PyObject *);
 extern PyTypeObject _PyTypeAlias_Type;
 extern PyTypeObject _PyNoDefault_Type;
 extern PyObject _Py_NoDefaultStruct;
-extern PyTypeObject _PyNoExtraItems_Type;
-extern PyObject _Py_NoExtraItemsStruct;
 
 #ifdef __cplusplus
 }
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 8c6cc2c08b68dc..d1c305b3b9c10c 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -41,7 +41,7 @@
 from typing import Self, LiteralString
 from typing import TypeAlias
 from typing import ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs
-from typing import TypeGuard, TypeIs, NoDefault, NoExtraItems
+from typing import TypeGuard, TypeIs, NoDefault
 import abc
 import textwrap
 import typing
diff --git a/Lib/typing.py b/Lib/typing.py
index 7c45563be720a3..268537b2f87136 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -40,7 +40,6 @@
     Generic,
     Union,
     NoDefault,
-    NoExtraItems,
 )
 
 # Please keep __all__ alphabetized within each category.
diff --git a/Modules/_typingmodule.c b/Modules/_typingmodule.c
index 89d2a956eeb721..e51279c808a2e1 100644
--- a/Modules/_typingmodule.c
+++ b/Modules/_typingmodule.c
@@ -70,9 +70,6 @@ _typing_exec(PyObject *m)
     if (PyModule_AddObjectRef(m, "NoDefault", (PyObject *)&_Py_NoDefaultStruct) < 0) {
         return -1;
     }
-    if (PyModule_AddObjectRef(m, "NoExtraItems", (PyObject *)&_Py_NoExtraItemsStruct) < 0) {
-        return -1;
-    }
     return 0;
 }
 
diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index 8ffa00c332dddb..cead6e69af5451 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -123,63 +123,6 @@ PyTypeObject _PyNoDefault_Type = {
 
 PyObject _Py_NoDefaultStruct = _PyObject_HEAD_INIT(&_PyNoDefault_Type);
 
-/* NoExtraItems: a marker object for TypedDict extra_items when it's unset. */
-
-static PyObject *
-NoExtraItems_repr(PyObject *op)
-{
-    return PyUnicode_FromString("typing.NoExtraItems");
-}
-
-static PyObject *
-NoExtraItems_reduce(PyObject *op, PyObject *Py_UNUSED(ignored))
-{
-    return PyUnicode_FromString("NoExtraItems");
-}
-
-static PyMethodDef noextraitems_methods[] = {
-    {"__reduce__", NoExtraItems_reduce, METH_NOARGS, NULL},
-    {NULL, NULL}
-};
-
-static PyObject *
-noextraitems_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
-{
-    if (PyTuple_GET_SIZE(args) || (kwargs && PyDict_GET_SIZE(kwargs))) {
-        PyErr_SetString(PyExc_TypeError, "NoExtraItemsType takes no arguments");
-        return NULL;
-    }
-    return (PyObject *)&_Py_NoExtraItemsStruct;
-}
-
-static void
-noextraitems_dealloc(PyObject *obj)
-{
-    /* This should never get called, but we also don't want to SEGV if
-     * we accidentally decref NoExtraItems out of existence. Instead,
-     * since NoExtraItems is an immortal object, re-set the reference count.
-     */
-    _Py_SetImmortal(obj);
-}
-
-PyDoc_STRVAR(noextraitems_doc,
-"NoExtraItemsType()\n"
-"--\n\n"
-"The type of the NoExtraItems singleton.");
-
-PyTypeObject _PyNoExtraItems_Type = {
-    PyVarObject_HEAD_INIT(&PyType_Type, 0)
-    "NoExtraItemsType",
-    .tp_dealloc = noextraitems_dealloc,
-    .tp_repr = NoExtraItems_repr,
-    .tp_flags = Py_TPFLAGS_DEFAULT,
-    .tp_doc = noextraitems_doc,
-    .tp_methods = noextraitems_methods,
-    .tp_new = noextraitems_new,
-};
-
-PyObject _Py_NoExtraItemsStruct = _PyObject_HEAD_INIT(&_PyNoExtraItems_Type);
-
 typedef struct {
     PyObject_HEAD
     PyObject *value;
diff --git a/Tools/c-analyzer/cpython/ignored.tsv b/Tools/c-analyzer/cpython/ignored.tsv
index f686a1f9a9a380..4fdb7b3cd1abf2 100644
--- a/Tools/c-analyzer/cpython/ignored.tsv
+++ b/Tools/c-analyzer/cpython/ignored.tsv
@@ -344,8 +344,6 @@ Objects/obmalloc.c	-	obmalloc_state_main	-
 Objects/obmalloc.c	-	obmalloc_state_initialized	-
 Objects/typeobject.c	-	name_op	-
 Objects/typeobject.c	-	slotdefs	-
-Objects/typevarobject.c	-	_PyNoExtraItems_Type	-
-Objects/typevarobject.c	-	_Py_NoExtraItemsStruct	-
 Objects/unicodeobject.c	-	stripfuncnames	-
 Objects/unicodeobject.c	-	utf7_category	-
 Objects/unicodeobject.c	unicode_decode_call_errorhandler_wchar	argparse	-

From 18b929bb058f591ef906c00adc87503daf492c24 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 25 Aug 2025 21:47:57 -0400
Subject: [PATCH 18/20] Update Lib/typing.py

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
---
 Lib/typing.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index 268537b2f87136..312f3d40fd58ac 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3275,7 +3275,7 @@ class DatabaseUser(TypedDict):
 
     The closed argument controls whether the TypedDict allows additional
     non-required items during inheritance and assignability checks.
-    If closed=True, the TypedDict is closed to additional items::
+    If closed=True, the TypedDict does not allow additional items::
 
         Point2D = TypedDict('Point2D', {'x': int, 'y': int}, closed=True)
         class Point3D(Point2D):

From 611b3e6c91afb71434dda8d832b67e695a8f52e7 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Mon, 25 Aug 2025 22:36:49 -0400
Subject: [PATCH 19/20] define NoExtraItems singleton in Python

---
 Lib/test/test_typing.py |  2 +-
 Lib/typing.py           | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index d1c305b3b9c10c..8362664f101055 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -34,7 +34,7 @@
 from typing import dataclass_transform
 from typing import no_type_check, no_type_check_decorator
 from typing import Type
-from typing import NamedTuple, NotRequired, Required, ReadOnly, TypedDict
+from typing import NamedTuple, NotRequired, Required, ReadOnly, TypedDict, NoExtraItems
 from typing import IO, TextIO, BinaryIO
 from typing import Pattern, Match
 from typing import Annotated, ForwardRef
diff --git a/Lib/typing.py b/Lib/typing.py
index 312f3d40fd58ac..8ba731efc939d0 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3056,6 +3056,20 @@ def _namedtuple_mro_entries(bases):
 NamedTuple.__mro_entries__ = _namedtuple_mro_entries
 
 
+class _NoExtraItemsType:
+    """The type of the NoExtraItems singleton."""
+
+    __slots__ = ()
+
+    def __repr__(self):
+        return 'typing.NoExtraItems'
+
+    def __reduce__(self):
+        return 'NoExtraItems'
+
+NoExtraItems = _NoExtraItemsType()
+
+
 def _get_typeddict_qualifiers(annotation_type):
     while True:
         annotation_origin = get_origin(annotation_type)

From a6250f4730796c65180d49839e7a8c872c27a104 Mon Sep 17 00:00:00 2001
From: Angela Liss <59097311+angela-tarantula@users.noreply.github.com>
Date: Tue, 26 Aug 2025 08:05:46 -0400
Subject: [PATCH 20/20] enforce singleton qualities on NoExtraItems

---
 Lib/typing.py | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index 8ba731efc939d0..cc506e6338b13d 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -3056,11 +3056,22 @@ def _namedtuple_mro_entries(bases):
 NamedTuple.__mro_entries__ = _namedtuple_mro_entries
 
 
-class _NoExtraItemsType:
+class _SingletonMeta(type):
+    def __setattr__(cls, attr, value):
+        # TypeError is consistent with the behavior of NoneType
+        raise TypeError(
+                f"cannot set {attr!r} attribute of immutable type {cls.__name__!r}"
+                )
+
+
+class _NoExtraItemsType(metaclass=_SingletonMeta):
     """The type of the NoExtraItems singleton."""
 
     __slots__ = ()
 
+    def __new__(cls):
+        return globals().get("NoExtraItems") or object.__new__(cls)
+
     def __repr__(self):
         return 'typing.NoExtraItems'
 
@@ -3068,6 +3079,8 @@ def __reduce__(self):
         return 'NoExtraItems'
 
 NoExtraItems = _NoExtraItemsType()
+del _NoExtraItemsType
+del _SingletonMeta
 
 
 def _get_typeddict_qualifiers(annotation_type):