BUG: nonexistent Timestamp pre-summer/winter DST w/dateutil timezone

doc/source/whatsnew/v1.1.0.rst

@@ -59,9 +59,10 @@ Categorical
 
 Datetimelike
 ^^^^^^^^^^^^
+
 - Bug in :class:`Timestamp` where constructing :class:`Timestamp` from ambiguous epoch time and calling constructor again changed :meth:`Timestamp.value` property (:issue:`24329`)
 - :meth:`DatetimeArray.searchsorted`, :meth:`TimedeltaArray.searchsorted`, :meth:`PeriodArray.searchsorted` not recognizing non-pandas scalars and incorrectly raising ``ValueError`` instead of ``TypeError`` (:issue:`30950`)
--
+- Bug in :class:`Timestamp` where constructing :class:`Timestamp` with dateutil timezone less than 128 nanoseconds before daylight saving time switch from winter to summer would result in nonexistent time (:issue:`31043`)
 
 Timedelta
 ^^^^^^^^^

pandas/_libs/tslibs/nattype.pyx

@@ -278,7 +278,7 @@ cdef class _NaT(datetime):
 
     def total_seconds(self):
         """
-        Total duration of timedelta in seconds (to ns precision).
+        Total duration of timedelta in seconds (to microsecond precision).
         """
         # GH#10939
         return np.nan

pandas/_libs/tslibs/timedeltas.pyx

@@ -861,9 +861,11 @@ cdef class _Timedelta(timedelta):
 
     def total_seconds(self):
         """
-        Total duration of timedelta in seconds (to ns precision).
+        Total duration of timedelta in seconds (to microsecond precision).
         """
-        return self.value / 1e9
+        # GH 31043
+        # Microseconds precision to avoid confusing tzinfo.utcoffset
+        return np.round((self.value - self.value % 1000) / 1e9, 6)
 
     def view(self, dtype):
         """

pandas/tests/indexes/datetimes/test_timezones.py

@@ -581,12 +581,7 @@ def test_dti_construction_ambiguous_endpoint(self, tz):
             ["US/Pacific", "shift_forward", "2019-03-10 03:00"],
             ["dateutil/US/Pacific", "shift_forward", "2019-03-10 03:00"],
             ["US/Pacific", "shift_backward", "2019-03-10 01:00"],
-            pytest.param(
-                "dateutil/US/Pacific",
-                "shift_backward",
-                "2019-03-10 01:00",
-                marks=pytest.mark.xfail(reason="GH 24329"),
-            ),
+            ["dateutil/US/Pacific", "shift_backward", "2019-03-10 01:00"],
             ["US/Pacific", timedelta(hours=1), "2019-03-10 03:00"],
         ],
     )

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -1092,3 +1092,17 @@ def test_constructor_ambigous_dst():
     expected = ts.value
     result = Timestamp(ts).value
     assert result == expected
+
+
+def test_constructor_before_dst_switch():
+    # GH 31043
+    # Make sure that calling Timestamp constructor
+    # on time just before DST switch doesn't lead to
+    # nonexistent time
+    epoch = 1552211999999999872
+    ts = Timestamp(epoch, tz="dateutil/US/Pacific")
+    delta = ts.replace(tzinfo=None) - datetime.utcfromtimestamp(0)
+    assert 1552183199.99 < delta.total_seconds() < 1552183200
+    expected = timedelta(seconds=0)
+    result = ts.tz.dst(ts)
+    assert result == expected