Issue #11004: Repair edge case in deque.count().

(Reviewed by Georg Brandl.)

Also made similar changes to deque.reverse() though this wasn't
strictly necessary (the edge case cannot occur with two pointers
moving to meet in the middle).  Making the change in reverse()
was more a matter of future-proofing.

1 files changed, 9 insertions, 0 deletions

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index da00c0d206..0dcadeb3c5 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -138,6 +138,15 @@ class TestBasic(unittest.TestCase):
         m.d = d
         self.assertRaises(RuntimeError, d.count, 3)
 
+        # test issue11004
+        # block advance failed after rotation aligned elements on right side of block
+        d = deque([None]*16)
+        for i in range(len(d)):
+            d.rotate(-1)
+        d.rotate(1)
+        self.assertEqual(d.count(1), 0)
+        self.assertEqual(d.count(None), 16)
+
     def test_comparisons(self):
         d = deque('xabc'); d.popleft()
         for e in [d, deque('abc'), deque('ab'), deque(), list(d)]: