From e973c61238807dcf4ccedc18a99db8f478c422c7 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Thu, 31 Jan 2008 01:42:11 +0000
Subject: [PATCH] Missing return

---
 Lib/_abcoll.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
index 75a80725282..89d41796b24 100644
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -293,6 +293,7 @@ class MutableSet(Set):
                 self.discard(value)
             else:
                 self.add(value)
+        return self
 
     def __isub__(self, it):
         for value in it: