commit 8110dbd470f3daa4de58dda66d360e3c26d3b94f
author Raymond Hettinger <rhettinger@users.noreply.github.com> Mon Sep 25 02:15:53 2017 -0700
committer GitHub <noreply@github.com> Mon Sep 25 02:15:53 2017 -0700
tree 1f5c602bcfbeedbc3cf2e6cfc86a5f44611b12a3
parent e6d9fcbb8d0c325e57df08ae8781aafedb71eca2

bpo-26491 Defer DECREFs until enumobject is in a consistent state (#3747)

Objects/enumobject.c

diff --git a/Objects/enumobject.c b/Objects/enumobject.c
index 3eb1736..154d901 100644
--- a/Objects/enumobject.c
+++ b/Objects/enumobject.c
@@ -103,6 +103,8 @@
     PyObject *result = en->en_result;
     PyObject *next_index;
     PyObject *stepped_up;
+    PyObject *old_index;
+    PyObject *old_item;
 
     if (en->en_longindex == NULL) {
         en->en_longindex = PyLong_FromSsize_t(PY_SSIZE_T_MAX);
@@ -118,15 +120,19 @@
 
     if (result->ob_refcnt == 1) {
         Py_INCREF(result);
-        Py_DECREF(PyTuple_GET_ITEM(result, 0));
-        Py_DECREF(PyTuple_GET_ITEM(result, 1));
-    } else {
-        result = PyTuple_New(2);
-        if (result == NULL) {
-            Py_DECREF(next_index);
-            Py_DECREF(next_item);
-            return NULL;
-        }
+        old_index = PyTuple_GET_ITEM(result, 0);
+        old_item = PyTuple_GET_ITEM(result, 1);
+        PyTuple_SET_ITEM(result, 0, next_index);
+        PyTuple_SET_ITEM(result, 1, next_item);
+        Py_DECREF(old_index);
+        Py_DECREF(old_item);
+        return result;
+    }
+    result = PyTuple_New(2);
+    if (result == NULL) {
+        Py_DECREF(next_index);
+        Py_DECREF(next_item);
+        return NULL;
     }
     PyTuple_SET_ITEM(result, 0, next_index);
     PyTuple_SET_ITEM(result, 1, next_item);
@@ -140,6 +146,8 @@
     PyObject *next_item;
     PyObject *result = en->en_result;
     PyObject *it = en->en_sit;
+    PyObject *old_index;
+    PyObject *old_item;
 
     next_item = (*Py_TYPE(it)->tp_iternext)(it);
     if (next_item == NULL)
@@ -157,15 +165,19 @@
 
     if (result->ob_refcnt == 1) {
         Py_INCREF(result);
-        Py_DECREF(PyTuple_GET_ITEM(result, 0));
-        Py_DECREF(PyTuple_GET_ITEM(result, 1));
-    } else {
-        result = PyTuple_New(2);
-        if (result == NULL) {
-            Py_DECREF(next_index);
-            Py_DECREF(next_item);
-            return NULL;
-        }
+        old_index = PyTuple_GET_ITEM(result, 0);
+        old_item = PyTuple_GET_ITEM(result, 1);
+        PyTuple_SET_ITEM(result, 0, next_index);
+        PyTuple_SET_ITEM(result, 1, next_item);
+        Py_DECREF(old_index);
+        Py_DECREF(old_item);
+        return result;
+    }
+    result = PyTuple_New(2);
+    if (result == NULL) {
+        Py_DECREF(next_index);
+        Py_DECREF(next_item);
+        return NULL;
     }
     PyTuple_SET_ITEM(result, 0, next_index);
     PyTuple_SET_ITEM(result, 1, next_item);