gh-141510: Optimize {frozen}dict.fromkeys for frozendict

Misc/NEWS.d/next/Core_and_Builtins/2026-02-17-22-27-11.gh-issue-141510.-4yYsf.rst

@@ -0,0 +1,3 @@
+Optimize :meth:`dict.fromkeys` and :meth:`frozendict.fromkeys` to avoid
+unnecessary thread-safety operations in frozendict cases. Patch by Donghee
+Na.

Objects/dictobject.c

@@ -3285,14 +3285,22 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
 
 
     if (PyAnyDict_CheckExact(d)) {
-        if (PyAnyDict_CheckExact(iterable)) {
+        if (PyDict_CheckExact(iterable)) {
             PyDictObject *mp = (PyDictObject *)d;
 
             Py_BEGIN_CRITICAL_SECTION2(d, iterable);
             d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
             Py_END_CRITICAL_SECTION2();
             return d;
         }
+        else if (PyFrozenDict_CheckExact(iterable)) {
+            PyDictObject *mp = (PyDictObject *)d;
+
+            Py_BEGIN_CRITICAL_SECTION(d);
+            d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
+            Py_END_CRITICAL_SECTION();
+            return d;
+        }
         else if (PyAnySet_CheckExact(iterable)) {
             PyDictObject *mp = (PyDictObject *)d;
 
@@ -3302,14 +3310,37 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
             return d;
         }
     }
+    else if (PyFrozenDict_CheckExact(d)) {
+        if (PyDict_CheckExact(iterable)) {
+            PyDictObject *mp = (PyDictObject *)d;
+
+            Py_BEGIN_CRITICAL_SECTION(iterable);
+            d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
+            Py_END_CRITICAL_SECTION();
+            return d;
+        }
+        else if (PyFrozenDict_CheckExact(iterable)) {
+            PyDictObject *mp = (PyDictObject *)d;
+            d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
+            return d;
+        }
+        else if (PyAnySet_CheckExact(iterable)) {
+            PyDictObject *mp = (PyDictObject *)d;
+
+            Py_BEGIN_CRITICAL_SECTION(iterable);
+            d = (PyObject *)dict_set_fromkeys(mp, iterable, value);
+            Py_END_CRITICAL_SECTION();
+            return d;
+        }
+    }
 
     it = PyObject_GetIter(iterable);
     if (it == NULL){
         Py_DECREF(d);
         return NULL;
     }
 
-    if (PyAnyDict_CheckExact(d)) {
+    if (PyDict_CheckExact(d)) {
         Py_BEGIN_CRITICAL_SECTION(d);
         while ((key = PyIter_Next(it)) != NULL) {
             status = setitem_lock_held((PyDictObject *)d, key, value);