Deque uses "len" instead of varhead in Py2.7
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index c5690ef..b41c5de 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -651,7 +651,7 @@
     Py_ssize_t n;
     PyObject *item;
 
-    if (Py_SIZE(deque) == 0)
+    if (deque->len == 0)
         return;
 
     /* During the process of clearing a deque, decrefs can cause the