Fixed #22598 -- Allowed make_aware() to work with ambiguous datetime

django/utils/timezone.py

@@ -347,7 +347,7 @@ def is_naive(value):
     return value.tzinfo is None or value.tzinfo.utcoffset(value) is None
 
 
-def make_aware(value, timezone=None):
+def make_aware(value, timezone=None, is_dst=None):
     """
     Makes a naive datetime.datetime in a given time zone aware.
     """
@@ -355,7 +355,7 @@ def make_aware(value, timezone=None):
         timezone = get_current_timezone()
     if hasattr(timezone, 'localize'):
         # This method is available for pytz time zones.
-        return timezone.localize(value, is_dst=None)
+        return timezone.localize(value, is_dst=is_dst)
     else:
         # Check that we won't overwrite the timezone of an aware datetime.
         if is_aware(value):

docs/ref/utils.txt

@@ -947,20 +947,37 @@ appropriate entities.
     Returns ``True`` if ``value`` is naive, ``False`` if it is aware. This
     function assumes that ``value`` is a :class:`~datetime.datetime`.
 
-.. function:: make_aware(value, timezone=None)
+.. function:: make_aware(value, timezone=None, is_dst=None)
 
     Returns an aware :class:`~datetime.datetime` that represents the same
     point in time as ``value`` in ``timezone``, ``value`` being a naive
     :class:`~datetime.datetime`. If ``timezone`` is set to ``None``, it
     defaults to the :ref:`current time zone <default-current-time-zone>`.
 
-    This function can raise an exception if ``value`` doesn't exist or is
-    ambiguous because of DST transitions.
+    When pytz_ is installed, the exception ``pytz.AmbiguousTimeError``
+    will be raised if you try to make ``value`` aware during a DST transition
+    where the same time occurs twice (when reverting from DST). Setting
+    ``is_dst`` to ``True`` or ``False`` will avoid the exception by choosing if
+    the time is pre-transition or post-transition respectively.
+
+    When pytz_ is installed, the exception ``pytz.NonExistentTimeError``
+    will be raised if you try to make ``value`` aware during a DST transition
+    such that the time never occurred (when entering into DST). Setting
+    ``is_dst`` to ``True`` or ``False`` will avoid the exception by moving the
+    hour backwards or forwards by 1 respectively. For example, ``is_dst=True``
+    would change a non-existent time of 2:30 to 1:30 and ``is_dst=False``
+    would change the time to 3:30.
+
+    ``is_dst`` has no effect when ``pytz`` is not installed.
 
     .. versionchanged:: 1.8
 
         In older versions of Django, ``timezone`` was a required argument.
 
+    .. versionchanged:: 1.9
+
+        The ``is_dst`` argument was added.
+
 .. function:: make_naive(value, timezone=None)
 
     Returns an naive :class:`~datetime.datetime` that represents in

docs/releases/1.9.txt

@@ -159,6 +159,9 @@ Internationalization
 * The :func:`django.views.i18n.javascript_catalog` view now works correctly
   if used multiple times with different configurations on the same page.
 
+* The :func:`django.utils.timezone.make_aware` function gained an ``is_dst``
+  argument to help resolve ambiguous times during DST transitions.
+
 Management Commands
 ^^^^^^^^^^^^^^^^^^^
 

tests/utils_tests/test_timezone.py

@@ -155,3 +155,37 @@ class TimezoneTests(unittest.TestCase):
             datetime.datetime(2011, 9, 1, 12, 20, 30))
         with self.assertRaises(ValueError):
             timezone.make_naive(datetime.datetime(2011, 9, 1, 12, 20, 30), CET)
+
+    @unittest.skipIf(pytz is None, "this test requires pytz")
+    def test_make_aware_pytz_ambiguous(self):
+        # 2:30 happens twice, once before DST ends and once after
+        ambiguous = datetime.datetime(2015, 10, 25, 2, 30)
+
+        with self.assertRaises(pytz.AmbiguousTimeError):
+            timezone.make_aware(ambiguous, timezone=CET)
+
+        std = timezone.make_aware(ambiguous, timezone=CET, is_dst=False)
+        dst = timezone.make_aware(ambiguous, timezone=CET, is_dst=True)
+        self.assertEqual(std - dst, datetime.timedelta(hours=1))
+        self.assertEqual(std.tzinfo.utcoffset(std), datetime.timedelta(hours=1))
+        self.assertEqual(dst.tzinfo.utcoffset(dst), datetime.timedelta(hours=2))
+
+    @unittest.skipIf(pytz is None, "this test requires pytz")
+    def test_make_aware_pytz_non_existent(self):
+        # 2:30 never happened due to DST
+        non_existent = datetime.datetime(2015, 3, 29, 2, 30)
+
+        with self.assertRaises(pytz.NonExistentTimeError):
+            timezone.make_aware(non_existent, timezone=CET)
+
+        std = timezone.make_aware(non_existent, timezone=CET, is_dst=False)
+        dst = timezone.make_aware(non_existent, timezone=CET, is_dst=True)
+        self.assertEqual(std - dst, datetime.timedelta(hours=1))
+        self.assertEqual(std.tzinfo.utcoffset(std), datetime.timedelta(hours=1))
+        self.assertEqual(dst.tzinfo.utcoffset(dst), datetime.timedelta(hours=2))
+
+        # round trip to UTC then back to CET
+        std = timezone.localtime(timezone.localtime(std, timezone.UTC()), CET)
+        dst = timezone.localtime(timezone.localtime(dst, timezone.UTC()), CET)
+        self.assertEqual((std.hour, std.minute), (3, 30))
+        self.assertEqual((dst.hour, dst.minute), (1, 30))