Merged revisions 84301 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r84301 | daniel.stutzbach | 2010-08-24 15:49:57 -0500 (Tue, 24 Aug 2010) | 1 line

  Issue 8750: Fixed MutableSet's methods to correctly handle reflexive operations, namely x -= x and x ^= x
........

1 files changed, 15 insertions, 9 deletions

diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
index e9234af382..73e668c11c 100644
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -305,18 +305,24 @@ class MutableSet(Set):
         return self
 
     def __ixor__(self, it):
-        if not isinstance(it, Set):
-            it = self._from_iterable(it)
-        for value in it:
-            if value in self:
-                self.discard(value)
-            else:
-                self.add(value)
+        if it is self:
+            self.clear()
+        else:
+            if not isinstance(it, Set):
+                it = self._from_iterable(it)
+            for value in it:
+                if value in self:
+                    self.discard(value)
+                else:
+                    self.add(value)
         return self
 
     def __isub__(self, it):
-        for value in it:
-            self.discard(value)
+        if it is self:
+            self.clear()
+        else:
+            for value in it:
+                self.discard(value)
         return self
 
 MutableSet.register(set)