Fix comparison across Daylight Savings Time boundary

pendulum/datetime.py

@@ -1310,22 +1310,28 @@ def __reduce__(self) -> tuple:
     def __reduce_ex__(self, protocol: int) -> tuple:
         return self.__class__, self._getstate(protocol)
 
-    def _cmp(self, other: datetime.datetime, **kwargs) -> int:
-        # Fix for pypy which compares using this method
-        # which would lead to infinite recursion if we didn't override
-        dt = datetime.datetime(
-            self.year,
-            self.month,
-            self.day,
-            self.hour,
-            self.minute,
-            self.second,
-            self.microsecond,
-            tzinfo=self.tz,
-            fold=self.fold,
-        )
-
-        return 0 if dt == other else 1 if dt > other else -1
+    def __le__(self, other):
+        if isinstance(other, DateTime):
+            return self._cmp(other) <= 0
+        return super().__le__(other)
+
+    def __lt__(self, other):
+        if isinstance(other, DateTime):
+            return self._cmp(other) < 0
+        return super().__lt__(other)
+
+    def __ge__(self, other):
+        # Will default to the negative of its reflection
+        return NotImplemented
+
+    def __gt__(self, other):
+        # Will default to the negative of its reflection
+        return NotImplemented
+
+    def _cmp(self, other, **kwargs):
+        sts = self.timestamp()
+        ots = other.timestamp()
+        return 0 if sts == ots else 1 if sts > ots else -1
 
 
 DateTime.min: DateTime = DateTime(1, 1, 1, 0, 0, tzinfo=UTC)

tests/datetime/test_comparison.py

@@ -1,8 +1,12 @@
 from __future__ import annotations
 
-from datetime import datetime
+from datetime import datetime, timedelta, tzinfo
+from dateutil import tz
+from pytz import timezone
 
 import pytz
+import pytest
+
 
 import pendulum
 
@@ -195,6 +199,95 @@ def test_less_than_with_timezone_false():
     assert not d1 < d3
 
 
+@pytest.mark.parametrize(
+    'truth_fun',
+    (
+        lambda earlier, later: earlier < later,
+        lambda earlier, later: earlier <= later,
+        lambda earlier, later: later > earlier,
+        lambda earlier, later: later >= earlier,
+    )
+)
+def test_comparison_crossing_dst_transitioning_off_pendulum_pendulum(truth_fun):
+    # We only need to test turning off DST, since that's when the time
+    # component goes backwards.
+    # We start with 2019-11-03T01:30:00-0700
+    earlier = pendulum.datetime(2019, 11, 3, 8, 30).in_tz("US/Pacific")
+    # Adding 55 minutes to it, we turn off DST, but the time component is
+    # slightly less than before, i.e. we get 2019-11-03T01:25:00-0800
+    later = earlier.add(minutes=55)
+    # Run through all inequality-comparison functions
+    assert truth_fun(earlier, later)
+
+
+@pytest.mark.parametrize(
+    'truth_fun',
+    (
+        lambda earlier, later: earlier < later,
+        lambda earlier, later: earlier <= later,
+        lambda earlier, later: later > earlier,
+        lambda earlier, later: later >= earlier,
+    )
+)
+def test_comparison_crossing_dst_transitioning_off_pendulum_datetime(truth_fun):
+    # We only need to test turning off DST, since that's when the time
+    # component goes backwards.
+    # We start with 2019-11-03T01:30:00-0700
+    earlier_pendulum = pendulum.datetime(2019, 11, 3, 8, 30).in_tz("US/Pacific")
+    us_pacific = timezone("US/Pacific")
+    earlier_datetime = datetime(2019, 11, 3, 1, 30, tzinfo=us_pacific)
+    # Adding 55 minutes to it, we turn off DST, but the time component is
+    # slightly less than before, i.e. we get 2019-11-03T01:25:00-0800
+    later_datetime = earlier_datetime + timedelta(minutes=55)
+    # Run through all inequality-comparison functions
+    assert truth_fun(earlier_pendulum, later_datetime)
+
+
+@pytest.mark.parametrize(
+    'truth_fun',
+    (
+        lambda earlier, later: earlier < later,
+        lambda earlier, later: earlier <= later,
+        lambda earlier, later: later > earlier,
+        lambda earlier, later: later >= earlier,
+    )
+)
+def test_comparison_crossing_dst_transitioning_off_datetime_pendulum(truth_fun):
+    # We only need to test turning off DST, since that's when the time
+    # component goes backwards.
+    # We start with 2019-11-03T01:30:00-0700
+    earlier_pendulum = pendulum.datetime(2019, 11, 3, 8, 30).in_tz("US/Pacific")
+    us_pacific = timezone("US/Pacific")
+    earlier_datetime = datetime(2019, 11, 3, 1, 30, tzinfo=us_pacific)
+    # Adding 55 minutes to it, we turn off DST, but the time component is
+    # slightly less than before, i.e. we get 2019-11-03T01:25:00-0800
+    later_pendulum = earlier_pendulum.add(minutes=55)
+    # Run through all inequality-comparison functions
+    assert truth_fun(earlier_datetime, later_pendulum)
+
+
+@pytest.mark.parametrize(
+    'truth_fun',
+    (
+        lambda earlier, later: earlier < later,
+        lambda earlier, later: earlier <= later,
+        lambda earlier, later: later > earlier,
+        lambda earlier, later: later >= earlier,
+    )
+)
+def test_comparison_crossing_dst_transitioning_off_datetime_datetime(truth_fun):
+    # We only need to test turning off DST, since that's when the time
+    # component goes backwards.
+    # We start with 2019-11-03T01:30:00-0700
+    us_pacific = timezone("US/Pacific")
+    earlier = datetime(2019, 11, 3, 1, 30, tzinfo=us_pacific)
+    # Adding 55 minutes to it, we turn off DST, but the time component is
+    # slightly less than before, i.e. we get 2019-11-03T01:25:00-0800
+    later = earlier + timedelta(minutes=55)
+    # Run through all inequality-comparison functions
+    assert truth_fun(earlier, later)
+
+
 def test_less_than_or_equal_true():
     d1 = pendulum.datetime(2000, 1, 1)
     d2 = pendulum.datetime(2000, 1, 2)