Implement and apply PEP 322, reverse iteration

6 files changed, 24 insertions, 8 deletions

diff --git a/Lib/heapq.py b/Lib/heapq.py
index 2c30b12..2223a97 100644
--- a/Lib/heapq.py
+++ b/Lib/heapq.py
@@ -165,7 +165,7 @@ def heapify(x):
     # or i < (n-1)/2.  If n is even = 2*j, this is (2*j-1)/2 = j-1/2 so
     # j-1 is the largest, which is n//2 - 1.  If n is odd = 2*j+1, this is
     # (2*j+1-1)/2 = j so j-1 is the largest, and that's again n//2-1.
-    for i in xrange(n//2 - 1, -1, -1):
+    for i in reversed(xrange(n//2)):
         _siftup(x, i)
 
 # 'heap' is a heap at all indices >= startpos, except possibly for pos.  pos
diff --git a/Lib/mhlib.py b/Lib/mhlib.py
index 5520f82..899939a 100644
--- a/Lib/mhlib.py
+++ b/Lib/mhlib.py
@@ -975,8 +975,7 @@ def test():
     print seqs
     f.putsequences(seqs)
     do('f.getsequences()')
-    testfolders.reverse()
-    for t in testfolders: do('mh.deletefolder(%s)' % `t`)
+    for t in reversed(testfolders): do('mh.deletefolder(%s)' % `t`)
     do('mh.getcontext()')
     context = mh.getcontext()
     f = mh.openfolder(context)
diff --git a/Lib/platform.py b/Lib/platform.py
index 31c47b4..389e50c 100755
--- a/Lib/platform.py
+++ b/Lib/platform.py
@@ -201,7 +201,7 @@ def _dist_try_harder(distname,version,id):
     if os.path.isdir('/usr/lib/setup'):
         # Check for slackware verson tag file (thanks to Greg Andruk)
         verfiles = os.listdir('/usr/lib/setup')
-        for n in range(len(verfiles)-1, -1, -1):
+        for n in reversed(xrange(len(verfiles))):
             if verfiles[n][:14] != 'slack-version-':
                 del verfiles[n]
         if verfiles:
diff --git a/Lib/random.py b/Lib/random.py
index 16b667a..1f279bb 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -253,7 +253,7 @@ class Random(_random.Random):
 
         if random is None:
             random = self.random
-        for i in xrange(len(x)-1, 0, -1):
+        for i in reversed(xrange(1, len(x))):
             # pick an element in x[:i+1] with which to exchange x[i]
             j = int(random() * (i+1))
             x[i], x[j] = x[j], x[i]
diff --git a/Lib/rfc822.py b/Lib/rfc822.py
index 4f69b22..9a52a90 100644
--- a/Lib/rfc822.py
+++ b/Lib/rfc822.py
@@ -421,8 +421,7 @@ class Message:
                 hit = 0
             if hit:
                 list.append(i)
-        list.reverse()
-        for i in list:
+        for i in reversed(list):
             del self.headers[i]
 
     def setdefault(self, name, default=""):
diff --git a/Lib/test/test_enumerate.py b/Lib/test/test_enumerate.py
index 88e24e8..b073606 100644
--- a/Lib/test/test_enumerate.py
+++ b/Lib/test/test_enumerate.py
@@ -124,9 +124,27 @@ class TestBig(EnumerateTestCase):
     seq = range(10,20000,2)
     res = zip(range(20000), seq)
 
+class TestReversed(unittest.TestCase):
+
+    def test_simple(self):
+        class A:
+            def __getitem__(self, i):
+                if i < 5:
+                    return str(i)
+                raise StopIteration
+            def __len__(self):
+                return 5
+        for data in 'abc', range(5), tuple(enumerate('abc')), A(), xrange(1,17,5):
+            self.assertEqual(list(data)[::-1], list(reversed(data)))
+        self.assertRaises(TypeError, reversed, {})
+
+    def test_xrange_optimization(self):
+        x = xrange(1)
+        self.assertEqual(type(reversed(x)), type(iter(x)))
 
 def test_main(verbose=None):
-    testclasses = (EnumerateTestCase, SubclassTestCase, TestEmpty, TestBig)
+    testclasses = (EnumerateTestCase, SubclassTestCase, TestEmpty, TestBig,
+                   TestReversed)
     test_support.run_unittest(*testclasses)
 
     # verify reference counting