gh-145056: Fix merging of collections.OrderedDict and frozendict

Author: serhiy-storchaka

Lib/collections/__init__.py

@@ -328,14 +328,14 @@ def __ior__(self, other):
         return self
 
     def __or__(self, other):
-        if not isinstance(other, dict):
+        if not isinstance(other, (dict, frozendict)):
             return NotImplemented
         new = self.__class__(self)
         new.update(other)
         return new
 
     def __ror__(self, other):
-        if not isinstance(other, dict):
+        if not isinstance(other, (dict, frozendict)):
             return NotImplemented
         new = self.__class__(other)
         new.update(self)

Lib/test/test_ordered_dict.py

@@ -698,6 +698,7 @@ def test_merge_operator(self):
         d |= list(b.items())
         expected = OrderedDict({0: 0, 1: 1, 2: 2, 3: 3})
         self.assertEqual(a | dict(b), expected)
+        self.assertEqual(a | frozendict(b), expected)
         self.assertEqual(a | b, expected)
         self.assertEqual(c, expected)
         self.assertEqual(d, expected)
@@ -706,12 +707,15 @@ def test_merge_operator(self):
         c |= a
         expected = OrderedDict({1: 1, 2: 1, 3: 3, 0: 0})
         self.assertEqual(dict(b) | a, expected)
+        self.assertEqual(frozendict(b) | a, expected)
         self.assertEqual(b | a, expected)
         self.assertEqual(c, expected)
 
         self.assertIs(type(a | b), OrderedDict)
         self.assertIs(type(dict(a) | b), OrderedDict)
+        self.assertIs(type(frozendict(a) | b), frozendict)  # BUG: should be OrderedDict
         self.assertIs(type(a | dict(b)), OrderedDict)
+        self.assertIs(type(a | frozendict(b)), OrderedDict)
 
         expected = a.copy()
         a |= ()

Misc/NEWS.d/next/Library/2026-03-26-14-51-55.gh-issue-145056.QS-6l1.rst

@@ -0,0 +1 @@
+Fix merging of :class:`collections.OrderedDict` and :class:`frozendict`.

Objects/odictobject.c

@@ -906,7 +906,7 @@ odict_or(PyObject *left, PyObject *right)
         type = Py_TYPE(right);
         other = left;
     }
-    if (!PyDict_Check(other)) {
+    if (!PyAnyDict_Check(other)) {
         Py_RETURN_NOTIMPLEMENTED;
     }
     PyObject *new = PyObject_CallOneArg((PyObject*)type, left);
@@ -2271,7 +2271,7 @@ static int
 mutablemapping_update_arg(PyObject *self, PyObject *arg)
 {
     int res = 0;
-    if (PyDict_CheckExact(arg)) {
+    if (PyAnyDict_CheckExact(arg)) {
         PyObject *items = PyDict_Items(arg);
         if (items == NULL) {
             return -1;