Tidied up the implementations of reversed (including the custom ones

for xrange and list objects).

* list.__reversed__ now checks the length of the sequence object before
  calling PyList_GET_ITEM() because the mutable could have changed length.

* all three implementations are now tranparent with respect to length and
  maintain the invariant len(it) == len(list(it)) even when the underlying
  sequence mutates.

* __builtin__.reversed() now frees the underlying sequence as soon
  as the iterator is exhausted.

* the code paths were rearranged so that the most common paths
  do not require a jump.

1 files changed, 2 insertions, 2 deletions

diff --git a/Lib/test/test_enumerate.py b/Lib/test/test_enumerate.py
index 34bc71db24..200779fb98 100644
--- a/Lib/test/test_enumerate.py
+++ b/Lib/test/test_enumerate.py
@@ -143,8 +143,8 @@ class TestReversed(unittest.TestCase):
 
     def test_len(self):
         # This is an implementation detail, not an interface requirement
-        s = 'hello'
-        self.assertEqual(len(reversed(s)), len(s))
+        for s in ('hello', tuple('hello'), list('hello'), xrange(5)):
+            self.assertEqual(len(reversed(s)), len(s))
 
 def test_main(verbose=None):
     testclasses = (EnumerateTestCase, SubclassTestCase, TestEmpty, TestBig,