From: Daniel Stutzbach <daniel@stutzbachenterprises.com>
Date: Tue, 24 Aug 2010 21:09:30 +0000 (+0000)
Subject: Merged revisions 84301 via svnmerge from
X-Git-Tag: v2.7.1rc1~366
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=9128732de668e5777e135a423d3fa8b9bbd71fe1;p=python

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
........
---

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)
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index f10f956f9b..16c4552e1d 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -526,6 +526,21 @@ class TestCollectionABCs(ABCTestCase):
         s = MySet([5,43,2,1])
         self.assertEqual(s.pop(), 1)
 
+    def test_issue8750(self):
+        empty = WithSet()
+        full = WithSet(range(10))
+        s = WithSet(full)
+        s -= s
+        self.assertEqual(s, empty)
+        s = WithSet(full)
+        s ^= s
+        self.assertEqual(s, empty)
+        s = WithSet(full)
+        s &= s
+        self.assertEqual(s, full)
+        s |= s
+        self.assertEqual(s, full)
+
     def test_Mapping(self):
         for sample in [dict]:
             self.assertIsInstance(sample(), Mapping)
diff --git a/Misc/NEWS b/Misc/NEWS
index 1e352bce9a..70ed097c66 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -31,6 +31,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #8750: Fixed MutableSet's methods to correctly handle
+  reflexive operations, namely x -= x and x ^= x.
+
 - Issue #9129: smtpd.py is vulnerable to DoS attacks deriving from missing 
   error handling when accepting a new connection.