Add fuzzy equality to Timespan

Now reports that a timespan is equal if the delta is less than
1ns

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

@@ -82,6 +82,24 @@ 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 overlaps(self, other: Timespan) -> Any:
         """Test whether this timespan overlaps another.
 

tests/test_timespan.py

@@ -92,6 +92,27 @@ 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)
+
     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'),