Fix an error when adding an interval to a pendulum instance across D…

…ST transition

pendulum/datetime.py

@@ -578,7 +578,7 @@ def _add_timedelta(self, delta):
 
         :rtype: DateTime
         """
-        if isinstance(delta, pendulum.Duration):
+        if isinstance(delta, pendulum.Period):
             return self.add(
                 years=delta.years,
                 months=delta.months,
@@ -589,9 +589,14 @@ def _add_timedelta(self, delta):
                 seconds=delta.remaining_seconds,
                 microseconds=delta.microseconds
             )
+        elif isinstance(delta, pendulum.Duration):
+            return self.add(
+                years=delta.years,
+                months=delta.months,
+                seconds=delta.total_seconds()
+            )
 
-        return self.add(days=delta.days, seconds=delta.seconds,
-                        microseconds=delta.microseconds)
+        return self.add(seconds=delta.total_seconds())
 
     def _subtract_timedelta(self, delta):
         """

pendulum/duration.py

@@ -64,10 +64,10 @@ def __new__(cls, days=0, seconds=0, microseconds=0,
         self._microseconds = round(total % m * 1e6)
         self._seconds = abs(int(total)) % SECONDS_PER_DAY * m
 
-        days = abs(int(total)) // SECONDS_PER_DAY * m
-        self._days = days + (years * 365 + months * 30)
-        self._remaining_days = abs(days) % 7 * m
-        self._weeks = abs(days) // 7 * m
+        _days = abs(int(total)) // SECONDS_PER_DAY * m
+        self._days = _days + (years * 365 + months * 30)
+        self._remaining_days = abs(_days) % 7 * m
+        self._weeks = abs(_days) // 7 * m
         self._months = months
         self._years = years
 

tests/datetime/test_add.py

@@ -248,3 +248,10 @@ def test_add_time_to_new_transition_repeated_big():
     assert dt.timezone_name == 'Europe/Paris'
     assert dt.offset == 3600
     assert not dt.is_dst()
+
+
+def test_add_interval():
+    dt = pendulum.datetime(2017, 3, 11, 10, 45, tz='America/Los_Angeles')
+    new = dt + pendulum.duration(hours=24)
+
+    assert_datetime(new, 2017, 3, 12, 11, 45)