From b952ab43f281bafd8d4fce4e84b41e655a3e7c23 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 1 Jun 2015 23:35:13 -0600
Subject: [PATCH] Issue #24359: Check for changed OrderedDict size during
 iteration.

---
 Lib/test/test_collections.py |  4 ----
 Misc/NEWS                    |  2 ++
 Objects/odictobject.c        | 10 ++++++++++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 097aa9afeae..7a1ff14b172 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -1746,10 +1746,6 @@ class OrderedDictTests:
         self.assertEqual(list(reversed(od.items())), list(reversed(pairs)))
 
     def test_detect_deletion_during_iteration(self):
-        # XXX This test should also work under cOrderedDict.
-        if self.module is c_coll:
-            raise unittest.SkipTest("only valid for pure Python OrderedDict")
-
         OrderedDict = self.module.OrderedDict
         od = OrderedDict.fromkeys('abc')
         it = iter(od)
diff --git a/Misc/NEWS b/Misc/NEWS
index 75186c86e7d..c0990ce531d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -19,6 +19,8 @@ Library
 
 - Issue #24348: Drop superfluous incref/decref.
 
+- Issue #24359: Check for changed OrderedDict size during iteration.
+
 
 What's New in Python 3.5.0 beta 2?
 ==================================
diff --git a/Objects/odictobject.c b/Objects/odictobject.c
index b91bd680bad..b44a61ef75a 100644
--- a/Objects/odictobject.c
+++ b/Objects/odictobject.c
@@ -1796,6 +1796,7 @@ typedef struct {
     PyObject_HEAD
     int kind;
     PyODictObject *di_odict;
+    Py_ssize_t di_size;
     PyObject *di_current;
     PyObject *di_result; /* reusable result tuple for iteritems */
 } odictiterobject;
@@ -1835,6 +1836,14 @@ odictiter_nextkey(odictiterobject *di)
     if (di->di_current == NULL)
         goto done;  /* We're already done. */
 
+    /* Check for unsupported changes. */
+    if (di->di_size != PyODict_SIZE(di->di_odict)) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "OrderedDict changed size during iteration");
+        di->di_size = -1; /* Make this state sticky */
+        return NULL;
+    }
+
     /* Get the key. */
     node = _odict_find_node(di->di_odict, di->di_current);
     if (node == NULL) {
@@ -2033,6 +2042,7 @@ odictiter_new(PyODictObject *od, int kind)
     node = reversed ? _odict_LAST(od) : _odict_FIRST(od);
     di->di_current = node ? _odictnode_KEY(node) : NULL;
     Py_XINCREF(di->di_current);
+    di->di_size = PyODict_SIZE(od);
     di->di_odict = od;
     Py_INCREF(od);