BUG: fix Timestamp constructor value change on DST Timestamp

Author: AlexKirko

pandas/_libs/tslibs/conversion.pyx

@@ -5,6 +5,8 @@ cimport numpy as cnp
 from numpy cimport int64_t, int32_t, intp_t, ndarray
 cnp.import_array()
 
+from dateutil import zoneinfo
+
 import pytz
 
 # stdlib datetime imports
@@ -382,6 +384,11 @@ cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
             obj.tzinfo = tz
     else:
         obj.value = pydatetime_to_dt64(ts, &obj.dts)
+        # GH 24329 Take DST offset into account
+        if isinstance(ts.tzinfo, zoneinfo.tzfile):
+            if ts.tzinfo.is_ambiguous(ts):
+                dst_offset = ts.tzinfo.dst(ts)
+                obj.value += int(dst_offset.total_seconds() * 1e9)
         obj.tzinfo = ts.tzinfo
 
     if obj.tzinfo is not None and not is_utc(obj.tzinfo):

pandas/tests/indexes/datetimes/test_timezones.py

@@ -573,13 +573,7 @@ def test_dti_construction_ambiguous_endpoint(self, tz):
             "2013-10-26 23:00", "2013-10-27 01:00", freq="H", tz=tz, ambiguous="infer"
         )
         assert times[0] == Timestamp("2013-10-26 23:00", tz=tz, freq="H")
-
-        if str(tz).startswith("dateutil"):
-            # fixed ambiguous behavior
-            # see GH#14621
-            assert times[-1] == Timestamp("2013-10-27 01:00:00+0100", tz=tz, freq="H")
-        else:
-            assert times[-1] == Timestamp("2013-10-27 01:00:00+0000", tz=tz, freq="H")
+        assert times[-1] == Timestamp("2013-10-27 01:00:00+0000", tz=tz, freq="H")
 
     @pytest.mark.parametrize(
         "tz, option, expected",

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -1081,3 +1081,13 @@ def test_dt_subclass_add_timedelta(lh, rh):
     result = lh + rh
     expected = SubDatetime(2000, 1, 1, 1)
     assert result == expected
+
+def test_constructor_ambigous_dst():
+    # GH 24329
+    # Make sure that calling Timestamp constructor
+    # on Timestamp created from ambiguous time
+    # doesn't change Timestamp.value
+    ts = Timestamp(1382835600000000000, tz='dateutil/Europe/London')
+    expected = ts.value
+    result = Timestamp(ts).value
+    assert result == expected