bpo-38525: Fix a segmentation fault when using reverse iterators of empty dict (GH-16846)

The reverse iterator for empty dictionaries was not handling correctly shared-key dictionaries.

1 files changed, 25 insertions, 0 deletions

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 13be857..5b51376 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1312,6 +1312,31 @@ class DictTest(unittest.TestCase):
         self.assertEqual(list(r), list('dcba'))
         self.assertRaises(StopIteration, next, r)
 
+    def test_reverse_iterator_for_empty_dict(self):
+        # bpo-38525: revered iterator should work properly
+
+        # empty dict is directly used for reference count test
+        self.assertEqual(list(reversed({})), [])
+        self.assertEqual(list(reversed({}.items())), [])
+        self.assertEqual(list(reversed({}.values())), [])
+        self.assertEqual(list(reversed({}.keys())), [])
+
+        # dict() and {} don't trigger the same code path
+        self.assertEqual(list(reversed(dict())), [])
+        self.assertEqual(list(reversed(dict().items())), [])
+        self.assertEqual(list(reversed(dict().values())), [])
+        self.assertEqual(list(reversed(dict().keys())), [])
+
+    def test_reverse_iterator_for_shared_shared_dicts(self):
+        class A:
+            def __init__(self, x, y):
+                if x: self.x = x
+                if y: self.y = y
+
+        self.assertEqual(list(reversed(A(1, 2).__dict__)), ['y', 'x'])
+        self.assertEqual(list(reversed(A(1, 0).__dict__)), ['x'])
+        self.assertEqual(list(reversed(A(0, 1).__dict__)), ['y'])
+
     def test_dict_copy_order(self):
         # bpo-34320
         od = collections.OrderedDict([('a', 1), ('b', 2)])