From: Raymond Hettinger <python@rcn.com>
Date: Mon, 8 Jan 2007 18:09:20 +0000 (+0000)
Subject: Fix zero-length corner case for iterating over a mutating deque.
X-Git-Tag: v2.6a1~2307
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=51c2f6cd180df4acd4eec6317b46ef38a2bebe16;p=python

Fix zero-length corner case for iterating over a mutating deque.
---

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index a562922993..35e1536532 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -396,6 +396,12 @@ class TestVariousIteratorArgs(unittest.TestCase):
         d.pop()
         self.assertRaises(RuntimeError, it.next)
 
+    def test_runtime_error_on_empty_deque(self):
+        d = deque()
+        it = iter(d)
+        d.append(10)
+        self.assertRaises(RuntimeError, it.next)
+
 class Deque(deque):
     pass
 
diff --git a/Modules/collectionsmodule.c b/Modules/collectionsmodule.c
index c1bd732b32..a0570cde37 100644
--- a/Modules/collectionsmodule.c
+++ b/Modules/collectionsmodule.c
@@ -911,15 +911,14 @@ dequeiter_next(dequeiterobject *it)
 {
 	PyObject *item;
 
-	if (it->counter == 0)
-		return NULL;
-
 	if (it->deque->state != it->state) {
 		it->counter = 0;
 		PyErr_SetString(PyExc_RuntimeError,
 				"deque mutated during iteration");
 		return NULL;
 	}
+	if (it->counter == 0)
+		return NULL;        
 	assert (!(it->b == it->deque->rightblock &&
 		  it->index > it->deque->rightindex));