From 07c52789e0e0df2f9e432f8897f6f3f87542041d Mon Sep 17 00:00:00 2001
From: tonghuaroot <tonghuaroot@gmail.com>
Date: Fri, 7 Aug 2026 18:20:59 +0800
Subject: [PATCH] gh-155324: Pickle frozendict with all protocols

frozendict only defined __getnewargs__, so pickling raised TypeError at
protocols 0 and 1. Give it a __reduce__ mirroring frozenset.
---
 Lib/test/test_dict.py                         | 21 +++++++---------
 ...-08-07-18-19-51.gh-issue-155324.Pk4Rz7.rst |  3 +++
 Objects/dictobject.c                          | 24 +++++++++++++++----
 3 files changed, 31 insertions(+), 17 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-18-19-51.gh-issue-155324.Pk4Rz7.rst

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index dc31d403b837ad..78342f809c11be 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1991,19 +1991,14 @@ def test_pickle(self):
                 if type(fd) == FrozenDictSlots:
                     fd.slot_attr = 456
                 with self.subTest(fd=fd, proto=proto):
-                    if proto >= 2:
-                        p = pickle.dumps(fd, proto)
-                        fd2 = pickle.loads(p)
-                        self.assertEqual(fd2, fd)
-                        self.assertEqual(type(fd2), type(fd))
-                        if type(fd) == FrozenDict:
-                            self.assertEqual(fd2.attr, 123)
-                        if type(fd) == FrozenDictSlots:
-                            self.assertEqual(fd2.slot_attr, 456)
-                    else:
-                        # protocol 0 and 1 don't support frozendict
-                        with self.assertRaises(TypeError):
-                            pickle.dumps(fd, proto)
+                    p = pickle.dumps(fd, proto)
+                    fd2 = pickle.loads(p)
+                    self.assertEqual(fd2, fd)
+                    self.assertEqual(type(fd2), type(fd))
+                    if type(fd) == FrozenDict:
+                        self.assertEqual(fd2.attr, 123)
+                    if type(fd) == FrozenDictSlots:
+                        self.assertEqual(fd2.slot_attr, 456)
 
     def test_pickle_iter(self):
         fd = frozendict(c=1, b=2, a=3, d=4, e=5, f=6)
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-18-19-51.gh-issue-155324.Pk4Rz7.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-18-19-51.gh-issue-155324.Pk4Rz7.rst
new file mode 100644
index 00000000000000..3eba2262dbe733
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-18-19-51.gh-issue-155324.Pk4Rz7.rst
@@ -0,0 +1,3 @@
+``frozendict`` can now be pickled with all pickle protocols, matching
+:class:`frozenset`. Previously protocols 0 and 1 raised :exc:`TypeError`.
+Patch by tonghuaroot.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index c650aa456d2cc9..f7caa48e66d993 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -8344,14 +8344,29 @@ _PyObject_InlineValuesConsistencyCheck(PyObject *obj)
 // --- frozendict implementation ---------------------------------------------
 
 static PyObject *
-frozendict_getnewargs(PyObject *op, PyObject *Py_UNUSED(dummy))
+frozendict_reduce(PyObject *op, PyObject *Py_UNUSED(dummy))
 {
-    // Call dict(op): convert 'op' frozendict to a dict
+    // Mirror frozenset.__reduce__ so frozendict pickles at every protocol
+    // (__getnewargs__ alone only works at protocol 2 and above).
+    // Call dict(op) to convert the frozendict to a dict argument.
     PyObject *arg = PyObject_CallOneArg((PyObject*)&PyDict_Type, op);
     if (arg == NULL) {
         return NULL;
     }
-    return Py_BuildValue("(N)", arg);
+    PyObject *args = PyTuple_Pack(1, arg);
+    Py_DECREF(arg);
+    if (args == NULL) {
+        return NULL;
+    }
+    PyObject *state = _PyObject_GetState(op);
+    if (state == NULL) {
+        Py_DECREF(args);
+        return NULL;
+    }
+    PyObject *result = PyTuple_Pack(3, Py_TYPE(op), args, state);
+    Py_DECREF(args);
+    Py_DECREF(state);
+    return result;
 }
 
 
@@ -8377,7 +8392,8 @@ static PyMethodDef frozendict_methods[] = {
     DICT___REVERSED___METHODDEF
     {"__class_getitem__", Py_GenericAlias, METH_O|METH_CLASS,
      PyDoc_STR("frozendicts are generic over two types, signifying (respectively) the types of the frozendict's keys and values")},
-    {"__getnewargs__", frozendict_getnewargs, METH_NOARGS},
+    {"__reduce__", frozendict_reduce, METH_NOARGS,
+     PyDoc_STR("Return state information for pickling.")},
     {NULL,              NULL}   /* sentinel */
 };