python · vstinner · Feb 18, 2026
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
@@ -1787,6 +1787,23 @@ 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))
+
+        # frozendict.fromkeys() must not call subclass constructor
+        class FrozenDictSubclass(frozendict):
+            def __new__(self):
+                raise ValueError("must not be called")
+
+        fd = FrozenDictSubclass.fromkeys("abc")
+        self.assertEqual(fd, frozendict(a=None, b=None, c=None))
+        self.assertEqual(type(fd), FrozenDictSubclass)
+
+        fd = FrozenDictSubclass.fromkeys(frozendict(x=1))
+        self.assertEqual(fd, frozendict(x=None))
+        self.assertEqual(type(fd), FrozenDictSubclass)
+

 if __name__ == "__main__":
    unittest.main()
@@ -3285,10 +3285,17 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
    PyObject *d;
    int status;

-    d = _PyObject_CallNoArgs(cls);
-    if (d == NULL)
+    if (PyObject_IsSubclass(cls, (PyObject*)&PyFrozenDict_Type)) {
+        // Never call frozendict subclass constructor which would call
+        // arbitrary Python code.
+        d = frozendict_new(_PyType_CAST(cls), NULL, NULL);
+    }
+    else {
+        d = _PyObject_CallNoArgs(cls);
+    }
+    if (d == NULL) {
        return NULL;
-
+    }

    if (PyDict_CheckExact(d)) {
        if (PyDict_CheckExact(iterable)) {
@@ -3359,7 +3366,7 @@ _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) {
            // anydict_setitem_take2 consumes a reference to key
            status = anydict_setitem_take2((PyDictObject *)d,
@@ -7994,6 +8001,8 @@ frozendict_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
    if (d == NULL) {
        return NULL;
    }
+    assert(Py_REFCNT(d) == 1);
+
    PyFrozenDictObject *self = _PyFrozenDictObject_CAST(d);
    self->ma_hash = -1;