From b9db9e152f3325b075e59ef4fdecfd0b9ec4746c Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Mon, 11 May 2015 19:58:56 -0700
Subject: [PATCH] Defend against a mutation during comparison

---
 Modules/_heapqmodule.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Modules/_heapqmodule.c b/Modules/_heapqmodule.c
index 38bcdbe72cf..04845f165aa 100644
--- a/Modules/_heapqmodule.c
+++ b/Modules/_heapqmodule.c
@@ -224,6 +224,11 @@ heappushpop(PyObject *self, PyObject *args)
         return item;
     }
 
+    if (PyList_GET_SIZE(heap) == 0) {
+        PyErr_SetString(PyExc_IndexError, "index out of range");
+        return NULL;
+    }
+
     returnitem = PyList_GET_ITEM(heap, 0);
     Py_INCREF(item);
     PyList_SET_ITEM(heap, 0, item);