[pypy-commit] pypy default: issue 1183: difference should never reuse the storage of a set as the storage of the resulting set, even if they are equal

[l.diekmann]

Author: Lukas Diekmann <lukas.diekmann at uni-duesseldorf.de>
Branch: 
Changeset: r55714:776e724afb92
Date: 2012-06-19 11:44 +0200
http://bitbucket.org/pypy/pypy/changeset/776e724afb92/

Log:	issue 1183: difference should never reuse the storage of a set as
	the storage of the resulting set, even if they are equal

diff --git a/pypy/objspace/std/setobject.py b/pypy/objspace/std/setobject.py
--- a/pypy/objspace/std/setobject.py
+++ b/pypy/objspace/std/setobject.py
@@ -491,7 +491,8 @@
             storage = self._difference_unwrapped(w_set, w_other)
         elif not w_set.strategy.may_contain_equal_elements(w_other.strategy):
             strategy = w_set.strategy
-            storage = w_set.sstorage
+            d = self.unerase(w_set.sstorage)
+            storage = self.erase(d.copy())
         else:
             strategy = self.space.fromcache(ObjectSetStrategy)
             storage = self._difference_wrapped(w_set, w_other)
diff --git a/pypy/objspace/std/test/test_setobject.py b/pypy/objspace/std/test/test_setobject.py
--- a/pypy/objspace/std/test/test_setobject.py
+++ b/pypy/objspace/std/test/test_setobject.py
@@ -642,6 +642,14 @@
         assert set([1,2,3,'5']).difference(set([2,3,4])) == set([1,'5'])
         assert set().difference(set([1,2,3])) == set()
 
+    def test_difference_bug(self):
+        a = set([1,2,3])
+        b = set([])
+        c = a - b
+        c.remove(2)
+        assert c == set([1, 3])
+        assert a == set([1,2, 3])
+
     def test_intersection_update(self):
         s = set([1,2,3,4,7])
         s.intersection_update([0,1,2,3,4,5,6])