Apply remove's mutation test after every equality test.

Lib/test/test_deque.py

@@ -19,11 +19,12 @@ class BadCmp:
         raise RuntimeError
 
 class MutateCmp:
-    def __init__(self, deque):
+    def __init__(self, deque, result):
         self.deque = deque
+        self.result = result
     def __eq__(self, other):
         self.deque.clear()
-        return True
+        return self.result
 
 class TestBasic(unittest.TestCase):
 
@@ -226,9 +227,9 @@ class TestBasic(unittest.TestCase):
             self.assert_(x is y)
 
         # Handle evil mutator
+        for match in (True, False):
             d = deque(['ab'])
-        d.extend([MutateCmp(d), 'c'])
-        e = deque(d)
+            d.extend([MutateCmp(d, match), 'c'])
             self.assertRaises(IndexError, d.remove, 'c')
             self.assertEqual(d, deque())
 

Modules/collectionsmodule.c

@@ -376,14 +376,14 @@ deque_remove(dequeobject *deque, PyObject *value)
 	for (i=0 ; i<n ; i++) {
 		PyObject *item = deque->leftblock->data[deque->leftindex];
 		int cmp = PyObject_RichCompareBool(item, value, Py_EQ);
-		if (cmp > 0) {
-			PyObject *tgt;
+
 		if (deque->len != n) {
 			PyErr_SetString(PyExc_IndexError, 
 				"deque mutated during remove().");
 			return NULL;
 		}
-			tgt = deque_popleft(deque, NULL);
+		if (cmp > 0) {
+			PyObject *tgt = deque_popleft(deque, NULL);
 			assert (tgt != NULL);
 			Py_DECREF(tgt);
 			if (_deque_rotate(deque, i) == -1)