Missing return

diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
index 75a807252827ebd50233758c5b8e517292cc0003..89d41796b24d2da741a14e1835e14d2a596b0cf9 100644 (file)
--- 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: