Fix Series[timedelta64]+DatetimeIndex[tz] bugs

ser + index lossed timezone
closes pandas-dev#13905

index + ser retained timezone but returned a DatetimeIndex

Author: jbrockmendel

pandas/core/indexes/datetimes.py

@@ -855,6 +855,9 @@ def _maybe_update_attributes(self, attrs):
         return attrs
 
     def _add_delta(self, delta):
+        if isinstance(delta, ABCSeries):
+            return NotImplemented
+
         from pandas import TimedeltaIndex
         name = self.name
 

pandas/core/ops.py

@@ -709,6 +709,15 @@ def wrapper(left, right, name=name, na_op=na_op):
 
         left, right = _align_method_SERIES(left, right)
 
+        if is_timedelta64_dtype(left) and isinstance(right, pd.DatetimeIndex):
+            # GH#13905
+            # Defer to DatetimeIndex/TimedeltaIndex operations where timezones
+            # are handled carefully.
+            result = op(pd.TimedeltaIndex(left), right)
+            return construct_result(left, result,
+                                    index=left.index, name=left.name,
+                                    dtype=result.dtype)
+
         converted = _Op.get_op(left, right, name, na_op)
 
         left, right = converted.left, converted.right

pandas/tests/indexes/datetimes/test_arithmetic.py

@@ -363,6 +363,21 @@ def test_datetimeindex_sub_timestamp_overflow(self):
             with pytest.raises(OverflowError):
                 dtimin - variant
 
+    @pytest.mark.parametrize('tz', [None, 'America/Chicago'])
+    def test_dti_add_series(self, tz):
+        # GH#13905
+        index = pd.DatetimeIndex(['2016-06-28 05:30', '2016-06-28 05:31'],
+                                 tz=tz)
+        ser = pd.Series([pd.Timedelta(seconds=5)] * 2,
+                        index=index)
+        expected = pd.Series(index + pd.Timedelta(seconds=5),
+                             index=index)
+        assert expected.dtype == index.dtype
+        res = ser + index
+        tm.assert_series_equal(res, expected)
+        res2 = index + ser
+        tm.assert_series_equal(res2, expected)
+
 
 # GH 10699
 @pytest.mark.parametrize('klass,assert_func', zip([Series, DatetimeIndex],