Fixed #16899 -- Backported the fix for http://bugs.python.org/issue9063 and added a test.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16980 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/utils/tzinfo.py

@@ -57,7 +57,9 @@ class LocalTimezone(tzinfo):
             return None
 
     def _isdst(self, dt):
-        tt = (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second, dt.weekday(), 0, -1)
+        tt = (dt.year, dt.month, dt.day,
+              dt.hour, dt.minute, dt.second,
+              dt.weekday(), 0, 0)
         try:
             stamp = time.mktime(tt)
         except (OverflowError, ValueError):

tests/regressiontests/utils/tzinfo.py

@@ -1,9 +1,35 @@
-import unittest
-
-from django.utils.tzinfo import FixedOffset
+import datetime
+import os
+import time
+from django.utils.tzinfo import FixedOffset, LocalTimezone
+from django.utils import unittest
 
 class TzinfoTests(unittest.TestCase):
 
+    @classmethod
+    def setUpClass(cls):
+        cls.old_TZ = os.environ.get('TZ')
+        os.environ['TZ'] = 'US/Eastern'
+
+        try:
+            # Check if a timezone has been set
+            time.tzset()
+            cls.tz_tests = True
+        except AttributeError:
+            # No timezone available. Don't run the tests that require a TZ
+            cls.tz_tests = False
+
+    @classmethod
+    def tearDownClass(cls):
+        if cls.old_TZ is None:
+            del os.environ['TZ']
+        else:
+            os.environ['TZ'] = cls.old_TZ
+
+        # Cleanup - force re-evaluation of TZ environment variable.
+        if cls.tz_tests:
+            time.tzset()
+
     def test_fixedoffset(self):
         self.assertEqual(repr(FixedOffset(0)), '+0000')
         self.assertEqual(repr(FixedOffset(60)), '+0100')
@@ -16,3 +42,21 @@ class TzinfoTests(unittest.TestCase):
         self.assertEqual(repr(FixedOffset(5.5*60)), '+0530')
         self.assertEqual(repr(FixedOffset(-.5*60)), '-0030')
         self.assertEqual(repr(FixedOffset(.5*60)), '+0030')
+
+    def test_16899(self):
+        if not self.tz_tests:
+            return
+        ts = 1289106000
+        # Midnight at the end of DST in US/Eastern: 2010-11-07T05:00:00Z
+        dt = datetime.datetime.utcfromtimestamp(ts)
+        # US/Eastern -- we force its representation to "EST"
+        tz = LocalTimezone(dt + datetime.timedelta(days=1))
+        self.assertEqual(
+                repr(datetime.datetime.fromtimestamp(ts - 3600, tz)),
+                'datetime.datetime(2010, 11, 7, 0, 0, tzinfo=EST)')
+        self.assertEqual(
+                repr(datetime.datetime.fromtimestamp(ts, tz)),
+                'datetime.datetime(2010, 11, 7, 1, 0, tzinfo=EST)')
+        self.assertEqual(
+                repr(datetime.datetime.fromtimestamp(ts + 3600, tz)),
+                'datetime.datetime(2010, 11, 7, 1, 0, tzinfo=EST)')