From 201b53247969160b5bbb9669b1ccb38f6966abe5 Mon Sep 17 00:00:00 2001
From: tangyuan0821 <tangyuan0821@email.cn>
Date: Thu, 25 Jun 2026 22:32:23 +0800
Subject: [PATCH 1/2] gh-144361: Fix NameError when type parameter default
 refers to a forward name

---
 Lib/typing.py                                 | 21 ++++++++++++++++---
 ...-06-25-22-30-00.gh-issue-144361.lL9mN2.rst |  4 ++++
 2 files changed, 22 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-06-25-22-30-00.gh-issue-144361.lL9mN2.rst

diff --git a/Lib/typing.py b/Lib/typing.py
index 1579f492003f748..fb4c7af4e06f950 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1099,7 +1099,12 @@ def _typevartuple_prepare_subst(self, alias, args):
         raise TypeError(f"Too few arguments for {alias};"
                         f" actual {alen}, expected at least {plen-1}")
     if left == alen - right and self.has_default():
-        replacement = _unpack_args(self.__default__)
+        try:
+            default = self.__default__
+        except NameError:
+            default = annotationlib.call_evaluate_function(
+                self.evaluate_default, annotationlib.Format.FORWARDREF)
+        replacement = _unpack_args(default)
     else:
         replacement = args[left: alen - right]
 
@@ -1125,7 +1130,12 @@ def _paramspec_prepare_subst(self, alias, args):
     params = alias.__parameters__
     i = params.index(self)
     if i == len(args) and self.has_default():
-        args = (*args, self.__default__)
+        try:
+            default = self.__default__
+        except NameError:
+            default = annotationlib.call_evaluate_function(
+                self.evaluate_default, annotationlib.Format.FORWARDREF)
+        args = (*args, default)
     if i >= len(args):
         raise TypeError(f"Too few arguments for {alias}")
     # Special case where Z[[int, str, bool]] == Z[int, str, bool] in PEP 612.
@@ -1185,7 +1195,12 @@ def _generic_class_getitem(cls, args):
         for param in parameters:
             prepare = getattr(param, '__typing_prepare_subst__', None)
             if prepare is not None:
-                args = prepare(cls, args)
+                try:
+                    args = prepare(cls, args)
+                except NameError:
+                    default = annotationlib.call_evaluate_function(
+                        param.evaluate_default, annotationlib.Format.FORWARDREF)
+                    args = (*args, default)
         _check_generic_specialization(cls, args)
 
         new_args = []
diff --git a/Misc/NEWS.d/next/Library/2026-06-25-22-30-00.gh-issue-144361.lL9mN2.rst b/Misc/NEWS.d/next/Library/2026-06-25-22-30-00.gh-issue-144361.lL9mN2.rst
new file mode 100644
index 000000000000000..a791b363ac32d42
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-25-22-30-00.gh-issue-144361.lL9mN2.rst
@@ -0,0 +1,4 @@
+Fix :exc:`NameError` when a type parameter default (PEP 696/PEP 749)
+refers to a name defined later in the module. Now three call sites in
+:mod:`typing` fall back to :func:`annotationlib.call_evaluate_function`
+with :data:`~annotationlib.Format.FORWARDREF` when eager evaluation fails.

From 2a0ffacf4175f850c64fb9a53581d90eacd5d4a0 Mon Sep 17 00:00:00 2001
From: tangyuan0821 <tangyuan0821@email.cn>
Date: Fri, 26 Jun 2026 09:46:59 +0800
Subject: [PATCH 2/2] gh-144361: Add tests for forward reference default in
 type parameters

---
 Lib/test/test_typing.py | 48 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index ed07503cd63f12b..740d32bfedd8fa7 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -823,6 +823,54 @@ def test_pickle(self):
                 self.assertEqual(z.__bound__, typevar.__bound__)
                 self.assertEqual(z.__default__, typevar.__default__)
 
+    def test_forward_reference_default_typevar(self):
+        ns = run_code(
+            """
+            class A[T, U = ForwardName]:
+                pass
+            """
+        )
+        U, A = ns["A"].__type_params__[1], ns["A"]
+        with self.assertRaises(NameError):
+            U.__default__
+        result = A[int]
+        self.assertIsInstance(result.__args__[0], type)
+        self.assertIs(int, result.__args__[0])
+        self.assertIsInstance(result.__args__[1], ForwardRef)
+        self.assertEqual(result.__args__[1].__forward_arg__, 'ForwardName')
+
+    def test_forward_reference_default_typevartuple(self):
+        ns = run_code(
+            """
+            class A[T, *Ts = ForwardName]:
+                pass
+            """
+        )
+        Ts, A = ns["A"].__type_params__[1], ns["A"]
+        with self.assertRaises(NameError):
+            Ts.__default__
+        result = A[int]
+        self.assertIsInstance(result.__args__[0], type)
+        self.assertIs(int, result.__args__[0])
+        self.assertIsInstance(result.__args__[1], ForwardRef)
+        self.assertEqual(result.__args__[1].__forward_arg__, 'ForwardName')
+
+    def test_forward_reference_default_paramspec(self):
+        ns = run_code(
+            """
+            class A[T, **P = ForwardName]:
+                pass
+            """
+        )
+        P, A = ns["A"].__type_params__[1], ns["A"]
+        with self.assertRaises(NameError):
+            P.__default__
+        result = A[int]
+        self.assertIsInstance(result.__args__[0], type)
+        self.assertIs(int, result.__args__[0])
+        self.assertIsInstance(result.__args__[1], ForwardRef)
+        self.assertEqual(result.__args__[1].__forward_arg__, 'ForwardName')
+
 
 def template_replace(templates: list[str], replacements: dict[str, list[str]]) -> list[tuple[str]]:
     """Renders templates with possible combinations of replacements.