https://github.com/python/cpython/commit/c582ff3c2508a8b1164ed861e4f304ba6a782546
commit: c582ff3c2508a8b1164ed861e4f304ba6a782546
branch: main
author: Victor Stinner <[email protected]>
committer: vstinner <[email protected]>
date: 2026-02-18T15:56:09Z
summary:
gh-141510: Fix frozendict.fromkeys() for subclasses (#144952)
Copy the frozendict if needed.
files:
M Lib/test/test_dict.py
M Objects/dictobject.c
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 21f8bb11071c90..1a8ae1cd42356e 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1787,6 +1787,34 @@ def test_hash(self):
with self.assertRaisesRegex(TypeError, "unhashable type: 'list'"):
hash(fd)
+ def test_fromkeys(self):
+ self.assertEqual(frozendict.fromkeys('abc'),
+ frozendict(a=None, b=None, c=None))
+
+ # Subclass which overrides the constructor
+ created = frozendict(x=1)
+ class FrozenDictSubclass(frozendict):
+ def __new__(self):
+ return created
+
+ fd = FrozenDictSubclass.fromkeys("abc")
+ self.assertEqual(fd, frozendict(x=1, a=None, b=None, c=None))
+ self.assertEqual(type(fd), FrozenDictSubclass)
+ self.assertEqual(created, frozendict(x=1))
+
+ fd = FrozenDictSubclass.fromkeys(frozendict(y=2))
+ self.assertEqual(fd, frozendict(x=1, y=None))
+ self.assertEqual(type(fd), FrozenDictSubclass)
+ self.assertEqual(created, frozendict(x=1))
+
+ # Subclass which doesn't override the constructor
+ class FrozenDictSubclass2(frozendict):
+ pass
+
+ fd = FrozenDictSubclass2.fromkeys("abc")
+ self.assertEqual(fd, frozendict(a=None, b=None, c=None))
+ self.assertEqual(type(fd), FrozenDictSubclass2)
+
if __name__ == "__main__":
unittest.main()
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 68602caf61401a..8d3c34f87e2afe 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -138,6 +138,7 @@ As a consequence of this, split keys have a maximum size of
16.
// Forward declarations
static PyObject* frozendict_new(PyTypeObject *type, PyObject *args,
PyObject *kwds);
+static int dict_merge(PyObject *a, PyObject *b, int override);
/*[clinic input]
@@ -294,6 +295,8 @@ can_modify_dict(PyDictObject *mp)
return PyUnstable_Object_IsUniquelyReferenced(_PyObject_CAST(mp));
}
else {
+ // Locking is only required if the dictionary is not
+ // uniquely referenced.
ASSERT_DICT_LOCKED(mp);
return 1;
}
@@ -3238,6 +3241,8 @@ _PyDict_Pop(PyObject *dict, PyObject *key, PyObject
*default_value)
static PyDictObject *
dict_dict_fromkeys(PyDictObject *mp, PyObject *iterable, PyObject *value)
{
+ assert(can_modify_dict(mp));
+
PyObject *oldvalue;
Py_ssize_t pos = 0;
PyObject *key;
@@ -3263,6 +3268,8 @@ dict_dict_fromkeys(PyDictObject *mp, PyObject *iterable,
PyObject *value)
static PyDictObject *
dict_set_fromkeys(PyDictObject *mp, PyObject *iterable, PyObject *value)
{
+ assert(can_modify_dict(mp));
+
Py_ssize_t pos = 0;
PyObject *key;
Py_hash_t hash;
@@ -3294,9 +3301,31 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable,
PyObject *value)
int status;
d = _PyObject_CallNoArgs(cls);
- if (d == NULL)
+ if (d == NULL) {
return NULL;
+ }
+ // If cls is a frozendict subclass with overridden constructor,
+ // copy the frozendict.
+ PyTypeObject *cls_type = _PyType_CAST(cls);
+ if (PyFrozenDict_Check(d)
+ && PyObject_IsSubclass(cls, (PyObject*)&PyFrozenDict_Type)
+ && cls_type->tp_new != frozendict_new)
+ {
+ // Subclass-friendly copy
+ PyObject *copy = frozendict_new(cls_type, NULL, NULL);
+ if (copy == NULL) {
+ Py_DECREF(d);
+ return NULL;
+ }
+ if (dict_merge(copy, d, 1) < 0) {
+ Py_DECREF(d);
+ Py_DECREF(copy);
+ return NULL;
+ }
+ Py_SETREF(d, copy);
+ }
+ assert(!PyFrozenDict_Check(d) || can_modify_dict((PyDictObject*)d));
if (PyDict_CheckExact(d)) {
if (PyDict_CheckExact(iterable)) {
@@ -3367,7 +3396,7 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable,
PyObject *value)
dict_iter_exit:;
Py_END_CRITICAL_SECTION();
}
- else if (PyFrozenDict_CheckExact(d)) {
+ else if (PyFrozenDict_Check(d)) {
while ((key = PyIter_Next(it)) != NULL) {
// setitem_take2_lock_held consumes a reference to key
status = setitem_take2_lock_held((PyDictObject *)d,
@@ -8002,6 +8031,8 @@ frozendict_new(PyTypeObject *type, PyObject *args,
PyObject *kwds)
if (d == NULL) {
return NULL;
}
+ assert(can_modify_dict(_PyAnyDict_CAST(d)));
+
PyFrozenDictObject *self = _PyFrozenDictObject_CAST(d);
self->ma_hash = -1;
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