Merge pull request #360 from lsst/tickets/DM-26445

DM-26445: Fix Timespan equality to be fuzzy

python/lsst/daf/butler/core/timespan.py

@@ -67,11 +67,11 @@ def __str__(self) -> str:
         if self.begin is None:
             head = "(-∞, "
         else:
-            head = f"[{self.begin}, "
+            head = f"[{self.begin.tai.isot}, "
         if self.end is None:
             tail = "∞)"
         else:
-            tail = f"{self.end})"
+            tail = f"{self.end.tai.isot})"
         return head + tail
 
     def __repr__(self) -> str:
@@ -82,6 +82,28 @@ def __repr__(self) -> str:
         end = tmpl.format(t=self.end) if self.end is not None else None
         return f"Timespan(begin={begin}, end={end})"
 
+    def __eq__(self, other: Any) -> bool:
+        # Include some fuzziness in equality because round tripping
+        # can introduce some drift at the picosecond level
+        # Butler is okay wih nanosecond precision
+        if not isinstance(other, type(self)):
+            return False
+
+        def compare_time(t1: Optional[astropy.time.Time], t2: Optional[astropy.time.Time]) -> bool:
+            if t1 is None and t2 is None:
+                return True
+            if t1 is None or t2 is None:
+                return False
+
+            return times_equal(t1, t2)
+
+        result = compare_time(self.begin, other.begin) and compare_time(self.end, other.end)
+        return result
+
+    def __ne__(self, other: Any) -> bool:
+        # Need to override the explicit parent class implementation
+        return not self.__eq__(other)
+
     def overlaps(self, other: Timespan) -> Any:
         """Test whether this timespan overlaps another.
 

tests/test_time_utils.py

@@ -26,6 +26,7 @@
 
 from astropy.time import Time, TimeDelta
 from lsst.daf.butler import time_utils
+from lsst.daf.butler.core.time_utils import astropy_to_nsec
 
 
 class TimeTestCase(unittest.TestCase):
@@ -120,6 +121,12 @@ def test_times_equal(self):
         self.assertFalse(time_utils.times_equal(time1, time2, 499))
         self.assertFalse(time_utils.times_equal(time2, time1, 499))
 
+        # UTC vs TAI
+        time1 = Time('2013-06-17 13:34:45.775000', scale='tai', format='iso')
+        time2 = Time('2013-06-17T13:34:10.775', scale='utc', format='isot')
+        self.assertTrue(time_utils.times_equal(time1, time2))
+        self.assertEqual(astropy_to_nsec(time1), astropy_to_nsec(time2))
+
 
 if __name__ == "__main__":
     unittest.main()

tests/test_timespan.py

@@ -92,6 +92,39 @@ def testOperationConsistency(self):
                     self.assertEqual(diffs1, (a,))
                     self.assertEqual(diffs2, (b,))
 
+    def testPrecision(self):
+        """Test that we only use nanosecond precision for equality."""
+        ts1 = self.timespans[-1]
+        ts2 = Timespan(begin=ts1.begin + astropy.time.TimeDelta(1e-10, format="sec"), end=ts1.end)
+        self.assertEqual(ts1, ts2)
+
+        self.assertEqual(Timespan(begin=None, end=None), Timespan(begin=None, end=None))
+        self.assertEqual(Timespan(begin=None, end=ts1.end), Timespan(begin=None, end=ts1.end))
+
+        ts2 = Timespan(begin=ts1.begin + astropy.time.TimeDelta(1e-8, format="sec"), end=ts1.end)
+        self.assertNotEqual(ts1, ts2)
+
+        ts2 = Timespan(begin=None, end=ts1.end)
+        self.assertNotEqual(ts1, ts2)
+
+        t1 = Timespan(begin=astropy.time.Time(2456461.0, val2=0.06580758101851847, format="jd", scale="tai"),
+                      end=astropy.time.Time(2456461.0, val2=0.06617994212962963, format="jd", scale="tai"))
+        t2 = Timespan(begin=astropy.time.Time(2456461.0, val2=0.06580758101851858, format="jd", scale="tai"),
+                      end=astropy.time.Time(2456461.0, val2=0.06617994212962963, format="jd", scale="tai"))
+        self.assertEqual(t1, t2)
+
+        # Ensure that == and != work properly
+        self.assertTrue(t1 == t2, f"Equality of {t1} and {t2}")
+        self.assertFalse(t1 != t2, f"Check != is false for {t1} and {t2}")
+
+    def testTimescales(self):
+        """Test time scale conversion occurs on comparison."""
+        ts1 = Timespan(begin=astropy.time.Time('2013-06-17 13:34:45.775000', scale='tai', format='iso'),
+                       end=astropy.time.Time('2013-06-17 13:35:17.947000', scale='tai', format='iso'))
+        ts2 = Timespan(begin=astropy.time.Time('2013-06-17T13:34:10.775', scale='utc', format='isot'),
+                       end=astropy.time.Time('2013-06-17T13:34:42.947', scale='utc', format='isot'))
+        self.assertEqual(ts1, ts2, f"Compare {ts1} with {ts2}")
+
 
 if __name__ == "__main__":
     unittest.main()