Fixes for NEWS. Add setdefault test and fix

Author: efimov-mikhail

Lib/test/test_dict.py

@@ -1602,20 +1602,25 @@ def __hash__(self):
             d.get(key2)
 
     def test_clear_at_lookup(self):
-        d = {}
-
         class X(object):
             def __hash__(self):
                 return 1
             def __eq__(self, other):
                 nonlocal d
                 d.clear()
 
+        d = {}
         for _ in range(10):
             d[X()] = None
 
         self.assertEqual(len(d), 1)
 
+        d = {}
+        for _ in range(10):
+            d.setdefault(X(), None)
+
+        self.assertEqual(len(d), 1)
+
 
 class CAPITest(unittest.TestCase):
 

Misc/NEWS.d/next/Core_and_Builtins/2025-10-24-20-42-33.gh-issue-140551.-9swrl.rst

@@ -1,2 +1,2 @@
-Fixed crash in :class:`dict` if :meth:`clear` is called at the lookup stage. Patch by
-Mikhail Efimov.
+Fixed crash in :class:`dict` if :meth:`dict.clear` is called at the lookup
+stage. Patch by Mikhail Efimov.

Objects/dictobject.c

@@ -1775,6 +1775,14 @@ static inline int
 insert_combined_dict(PyInterpreterState *interp, PyDictObject *mp,
                      Py_hash_t hash, PyObject *key, PyObject *value)
 {
+    // gh-140551: If dict was cleaned in _Py_dict_lookup,
+    // we have to resize one more time to force general key kind.
+    if (DK_IS_UNICODE(mp->ma_keys) && !PyUnicode_CheckExact(key)) {
+        if (insertion_resize(mp, 0) < 0)
+            return -1;
+        assert(mp->ma_keys->dk_kind == DICT_KEYS_GENERAL);
+    }
+
     if (mp->ma_keys->dk_usable <= 0) {
         /* Need to resize. */
         if (insertion_resize(mp, 1) < 0) {
@@ -1899,14 +1907,6 @@ insertdict(PyInterpreterState *interp, PyDictObject *mp,
     if (ix == DKIX_ERROR)
         goto Fail;
 
-    // gh-140551: If dict was cleaned in _Py_dict_lookup,
-    // we have to resize one more time to force general key kind.
-    if (DK_IS_UNICODE(mp->ma_keys) && !PyUnicode_CheckExact(key)) {
-        if (insertion_resize(mp, 0) < 0)
-            goto Fail;
-        assert(mp->ma_keys->dk_kind == DICT_KEYS_GENERAL);
-    }
-
     if (ix == DKIX_EMPTY) {
         assert(!_PyDict_HasSplitTable(mp));
         /* Insert into new slot. */