From cc0269334fdf7be12de79316882befd5cdb4cf7e Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Mon, 1 Jun 2026 16:26:49 +0300
Subject: [PATCH] gh-149534: Fix unification of `defaultdict` and `frozendict`
 with `|` (#149539)

---
 Lib/test/test_defaultdict.py                         | 12 ++++++++++++
 .../2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst   |  1 +
 Modules/_collectionsmodule.c                         |  2 +-
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst

diff --git a/Lib/test/test_defaultdict.py b/Lib/test/test_defaultdict.py
index a193eb10f16..cc78f01e3e2 100644
--- a/Lib/test/test_defaultdict.py
+++ b/Lib/test/test_defaultdict.py
@@ -186,6 +186,18 @@ def test_union(self):
         with self.assertRaises(TypeError):
             i |= None
 
+        # frozendict
+        i_fd = i | frozendict(s)
+        self.assertIs(type(i_fd), defaultdict)
+        self.assertIs(i_fd.default_factory, int)
+        self.assertDictEqual(i_fd, {1: "one", 2: 2, 0: "zero"})
+        self.assertEqual(list(i_fd), [1, 2, 0])
+
+        fd_i = frozendict(s) | i
+        self.assertIs(type(fd_i), frozendict)
+        self.assertEqual(fd_i, {1: "one", 2: 2, 0: "zero"})
+        self.assertEqual(list(fd_i), [0, 1, 2])
+
     def test_factory_conflict_with_set_value(self):
         key = "conflict_test"
         count = 0
diff --git a/Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst b/Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst
new file mode 100644
index 00000000000..0938935a75d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-08-09-11-48.gh-issue-149534.Tw7eeY.rst
@@ -0,0 +1 @@
+Fix merging of :class:`collections.defaultdict` and :class:`frozendict`.
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index d702d655a40..541ca48633b 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -2421,7 +2421,7 @@ defdict_or(PyObject* left, PyObject* right)
         self = right;
         other = left;
     }
-    if (!PyDict_Check(other)) {
+    if (!PyAnyDict_Check(other)) {
         Py_RETURN_NOTIMPLEMENTED;
     }
     // Like copy(), this calls the object's class.