bpo-34573: Simplify __reduce__() of set and dict iterators. (GH-9050)

Simplify the pickling of set and dictionary objects iterators by consuming
the iterator into a list with PySequence_List.

Objects/dictobject.c

@@ -3663,44 +3663,14 @@ PyTypeObject PyDictIterItem_Type = {
 static PyObject *
 dictiter_reduce(dictiterobject *di, PyObject *Py_UNUSED(ignored))
 {
-    PyObject *list;
-    dictiterobject tmp;
-
-    list = PyList_New(0);
-    if (!list)
-        return NULL;
-
-    /* copy the itertor state */
-    tmp = *di;
+    /* copy the iterator state */
+    dictiterobject tmp = *di;
     Py_XINCREF(tmp.di_dict);
 
     /* iterate the temporary into a list */
-    for(;;) {
-        PyObject *element = 0;
-        if (Py_TYPE(di) == &PyDictIterItem_Type)
-            element = dictiter_iternextitem(&tmp);
-        else if (Py_TYPE(di) == &PyDictIterKey_Type)
-            element = dictiter_iternextkey(&tmp);
-        else if (Py_TYPE(di) == &PyDictIterValue_Type)
-            element = dictiter_iternextvalue(&tmp);
-        else
-            Py_UNREACHABLE();
-        if (element) {
-            if (PyList_Append(list, element)) {
-                Py_DECREF(element);
-                Py_DECREF(list);
-                Py_XDECREF(tmp.di_dict);
-                return NULL;
-            }
-            Py_DECREF(element);
-        } else
-            break;
-    }
+    PyObject *list = PySequence_List((PyObject*)&tmp);
     Py_XDECREF(tmp.di_dict);
-    /* check for error */
-    if (tmp.di_dict != NULL) {
-        /* we have an error */
-        Py_DECREF(list);
+    if (list == NULL) {
         return NULL;
     }
     return Py_BuildValue("N(N)", _PyObject_GetBuiltin("iter"), list);

Objects/setobject.c

@@ -843,36 +843,14 @@ static PyObject *setiter_iternext(setiterobject *si);
 static PyObject *
 setiter_reduce(setiterobject *si, PyObject *Py_UNUSED(ignored))
 {
-    PyObject *list;
-    setiterobject tmp;
-
-    list = PyList_New(0);
-    if (!list)
-        return NULL;
-
     /* copy the iterator state */
-    tmp = *si;
+    setiterobject tmp = *si;
     Py_XINCREF(tmp.si_set);
 
     /* iterate the temporary into a list */
-    for(;;) {
-        PyObject *element = setiter_iternext(&tmp);
-        if (element) {
-            if (PyList_Append(list, element)) {
-                Py_DECREF(element);
-                Py_DECREF(list);
-                Py_XDECREF(tmp.si_set);
-                return NULL;
-            }
-            Py_DECREF(element);
-        } else
-            break;
-    }
+    PyObject *list = PySequence_List((PyObject*)&tmp);
     Py_XDECREF(tmp.si_set);
-    /* check for error */
-    if (tmp.si_set != NULL) {
-        /* we have an error */
-        Py_DECREF(list);
+    if (list == NULL) {
         return NULL;
     }
     return Py_BuildValue("N(N)", _PyObject_GetBuiltin("iter"), list);