Makes PRE_TRANSITION rule no longer create a time in a DST gap.

Author: sdispater

docs/_docs/timezones.rst

@@ -43,7 +43,7 @@ given timezone to properly handle any transition that might have occurred.
         pendulum.set_transition_rule(pendulum.PRE_TRANSITION)
 
         pendulum.create(2013, 3, 31, 2, 30, 0, 0, 'Europe/Paris')
-        '2013-03-31T02:30:00+01:00'
+        '2013-03-31T01:30:00+01:00'
         pendulum.create(2013, 10, 27, 2, 30, 0, 0, 'Europe/Paris')
         '2013-10-27T02:30:00+02:00'
 
@@ -75,7 +75,7 @@ given timezone to properly handle any transition that might have occurred.
 
         dt = Pendulum(2013, 3, 31, 2, 30, 0, 0, 'Europe/Paris', fold=0)
         dt.isoformat()
-        '2013-03-31T02:30:00+01:00'
+        '2013-03-31T01:30:00+01:00'
 
         dt = Pendulum(2013, 3, 31, 2, 30, 0, 0, 'Europe/Paris', fold=1)
         dt.isoformat()
@@ -94,7 +94,7 @@ Shifting time to transition
 
 So, what happens when you add time to a ``Pendulum`` instance and stumble upon
 a transition time?
-Well, ``Pendulum``, provided with the context of the previous instance, will
+Well ``Pendulum``, provided with the context of the previous instance, will
 adopt the proper behavior and apply the transition accordingly.
 
 .. code-block:: python
@@ -161,7 +161,7 @@ when adding and subtracting time around transition times.
         # By default, fold is set to 0
         dt = paris.convert(dt)
         dt.isoformat()
-        '2013-03-31T02:30:00+01:00'
+        '2013-03-31T01:30:00+01:00'
 
         dt = datetime(2013, 3, 31, 2, 30, fold=1)
         dt = paris.convert(dt)
@@ -229,7 +229,7 @@ when adding and subtracting time around transition times.
         dt = datetime(2013, 3, 31, 2, 30)
         dt = tz.convert(dt, dst_rule=tz.PRE_TRANSITION)
         dt.isoformat()
-        '2013-03-31T02:30:00+01:00'
+        '2013-03-31T01:30:00+01:00'
         tz.convert(dt, dst_rule=tz.TRANSITION_ERROR)
         # NonExistingTime: The datetime 2013-03-31 02:30:00 does not exist.
 

pendulum/tz/timezone.py

@@ -219,7 +219,7 @@ def _normalize(self, dt, dst_rule=None):
                 elif dst_rule == self.PRE_TRANSITION:
                     # We do not apply the transition
                     (unix_time,
-                     tzinfo_index) = self._get_previous_transition_time(tr, dt)
+                     tzinfo_index) = self._get_previous_transition_time(tr, dt, skipped=True)
                 else:
                     unix_time = tr.unix_time - (tr.pre_time - dt).total_seconds()
         elif tr is end:
@@ -246,7 +246,7 @@ def _normalize(self, dt, dst_rule=None):
                 elif dst_rule == self.PRE_TRANSITION:
                     # We do not apply the transition
                     (unix_time,
-                     tzinfo_index) = self._get_previous_transition_time(tr, dt)
+                     tzinfo_index) = self._get_previous_transition_time(tr, dt, skipped=True)
                 else:
                     unix_time = tr.unix_time - (tr.pre_time - dt).total_seconds()
             elif tr.time <= dt <= tr.pre_time:
@@ -349,7 +349,7 @@ def _find_transition_index(self, dt, prop='_time'):
 
         return lo
 
-    def _get_previous_transition_time(self, tr, dt):
+    def _get_previous_transition_time(self, tr, dt, skipped=False):
         """
         Returns the time before the transition
         as a (unix_time, tzinfo_index) tuple.
@@ -360,6 +360,9 @@ def _get_previous_transition_time(self, tr, dt):
         :param dt: The datetime
         :type dt: datetime
 
+        :param skipped: Whether we are in a gap or not
+        :type skipped: bool
+
         :rtype: tuple
         """
         diff = self._get_diff(tr.pre_time, dt)
@@ -370,6 +373,13 @@ def _get_previous_transition_time(self, tr, dt):
 
         unix_time = tr.unix_time + diff
 
+        if skipped:
+            # If skipped time, we round down
+            # Only occurs when PRE_TRANSITION is used
+            forward = (self._tzinfos[tr.tzinfo_index].offset
+                       - self._tzinfos[tzinfo_index].offset)
+            unix_time -= forward
+
         return unix_time, tzinfo_index
 
     def tzname(self, dt):

tests/pendulum_tests/test_construct.py

@@ -196,12 +196,12 @@ def test_init_fold_is_honored_if_explicit(self):
         Pendulum.set_transition_rule(PRE_TRANSITION)
 
         d = Pendulum(2013, 3, 31, 2, 30, tzinfo='Europe/Paris')
-        self.assertPendulum(d, 2013, 3, 31, 2, 30)
+        self.assertPendulum(d, 2013, 3, 31, 1, 30)
 
         Pendulum.set_transition_rule(POST_TRANSITION)
 
         d = Pendulum(2013, 3, 31, 2, 30, tzinfo='Europe/Paris', fold=0)
-        self.assertPendulum(d, 2013, 3, 31, 2, 30)
+        self.assertPendulum(d, 2013, 3, 31, 1, 30)
 
         d = Pendulum(2013, 3, 31, 2, 30, tzinfo='Europe/Paris', fold=1)
         self.assertPendulum(d, 2013, 3, 31, 3, 30)

tests/pendulum_tests/test_fluent_setters.py

@@ -174,7 +174,7 @@ def test_replace_tzinfo_dst_with_pre_transition_rule(self):
         d = Pendulum.create(2013, 3, 31, 2, 30)
         new = d.replace(tzinfo='Europe/Paris')
 
-        self.assertPendulum(new, 2013, 3, 31, 2, 30)
+        self.assertPendulum(new, 2013, 3, 31, 1, 30)
         self.assertFalse(new.is_dst)
         self.assertEqual(new.offset, 3600)
         self.assertEqual(new.timezone_name, 'Europe/Paris')

tests/tz_tests/test_timezone.py

@@ -54,7 +54,7 @@ def test_skipped_time_with_pre_rule(self):
         self.assertEqual(2013, dt.year)
         self.assertEqual(3, dt.month)
         self.assertEqual(31, dt.day)
-        self.assertEqual(2, dt.hour)
+        self.assertEqual(1, dt.hour)
         self.assertEqual(30, dt.minute)
         self.assertEqual(45, dt.second)
         self.assertEqual(123456, dt.microsecond)
@@ -143,7 +143,7 @@ def test_create_uses_transition_rule(self):
         self.assertEqual(2013, dt.year)
         self.assertEqual(3, dt.month)
         self.assertEqual(31, dt.day)
-        self.assertEqual(2, dt.hour)
+        self.assertEqual(1, dt.hour)
         self.assertEqual(30, dt.minute)
         self.assertEqual(45, dt.second)
         self.assertEqual(123456, dt.microsecond)