Fix an error when subtracting two pendulum instances in the same timezone

Author: sdispater

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed an error when adding intervals to a Pendulum instance across DST transition.
+- Fixed an error when subtracting two pendulum instances in the same timezone.
 
 
 ## [1.4.2] - 2018-02-22

pendulum/helpers.py

@@ -159,9 +159,7 @@ def precise_diff(d1, d2):
         d1, d2 = d2, d1
         sign = -1
 
-    y_diff = d2.year - d1.year
-    m_diff = d2.month - d1.month
-    d_diff = d2.day - d1.day
+    d_diff = 0
     hour_diff = 0
     min_diff = 0
     sec_diff = 0
@@ -170,6 +168,7 @@ def precise_diff(d1, d2):
         _day_number(d2.year, d2.month, d2.day)
         - _day_number(d1.year, d1.month, d1.day)
     )
+
     in_same_tz = False
     tz1 = None
     tz2 = None
@@ -228,6 +227,14 @@ def precise_diff(d1, d2):
             hour_diff += 24
             d_diff -= 1
 
+    if d1 > d2:
+        d1, d2 = d2, d1
+        sign = -1
+
+    y_diff = d2.year - d1.year
+    m_diff = d2.month - d1.month
+    d_diff += d2.day - d1.day
+
     if d_diff < 0:
         year = d2.year
         month = d2.month

tests/pendulum_tests/test_add.py

@@ -237,6 +237,14 @@ def test_add_time_to_new_transition_does_not_use_transition_rule(self):
         self.assertEqual(7200, dt.offset)
         self.assertTrue(dt.is_dst)
 
+    def test_period_over_midnight_tz(self):
+        start = pendulum.create(2018, 2, 25, tz='Europe/Paris')
+        end = start.add(hours=1)
+        period = end - start
+        new_end = start + period
+
+        assert new_end == end
+
     def test_add_interval(self):
         dt = pendulum.create(2017, 3, 11, 10, 45, tz='America/Los_Angeles')
         new = dt + pendulum.interval(hours=24)