1 files changed, 20 insertions, 0 deletions
diff --git a/Lib/test/test_set.py b/Lib/test/test_set.py
index 2a791e4..8a43109 100644
--- a/Lib/test/test_set.py
+++ b/Lib/test/test_set.py
@@ -26,6 +26,14 @@ class ReprWrapper:
     def __repr__(self):
         return repr(self.value)
 
+class HashCountingInt(int):
+    'int-like object that counts the number of times __hash__ is called'
+    def __init__(self, *args):
+        self.hash_count = 0
+    def __hash__(self):
+        self.hash_count += 1
+        return int.__hash__(self)
+
 class TestJointOps(unittest.TestCase):
     # Tests common to both set and frozenset
 
@@ -273,6 +281,18 @@ class TestJointOps(unittest.TestCase):
             fo.close()
             os.remove(test_support.TESTFN)
 
+    def test_do_not_rehash_dict_keys(self):
+        n = 10
+        d = dict.fromkeys(map(HashCountingInt, xrange(n)))
+        self.assertEqual(sum(elem.hash_count for elem in d), n)
+        s = self.thetype(d)
+        self.assertEqual(sum(elem.hash_count for elem in d), n)
+        s.difference(d)
+        self.assertEqual(sum(elem.hash_count for elem in d), n)    
+        if hasattr(s, 'symmetric_difference_update'):
+            s.symmetric_difference_update(d)
+        self.assertEqual(sum(elem.hash_count for elem in d), n)      
+
 class TestSet(TestJointOps):
     thetype = set