BUG: Right result for DatetimeIndex + TimeDelta when timezone is set(pandas-dev#13905)

Author: conquistador1492

doc/source/whatsnew/v0.19.0.txt

@@ -938,6 +938,7 @@ Bug Fixes
 - Bug in invalid ``Timedelta`` arithmetic and comparison may raise ``ValueError`` rather than ``TypeError`` (:issue:`13624`)
 - Bug in invalid datetime parsing in ``to_datetime`` and ``DatetimeIndex`` may raise ``TypeError`` rather than ``ValueError`` (:issue:`11169`, :issue:`11287`)
 - Bug in ``Index`` created with tz-aware ``Timestamp`` and mismatched ``tz`` option incorrectly coerces timezone (:issue:`13692`)
+- Bug in ``DatetimeIndex + TimeDelta`` gives wrong results when timezone is set (:issue:`13905`)
 - Bug in ``DatetimeIndex`` with nanosecond frequency does not include timestamp specified with ``end`` (:issue:`13672`)
 
 - Bug in ``Index`` raises ``OutOfBoundsDatetime`` if ``datetime`` exceeds ``datetime64[ns]`` bounds, rather than coercing to ``object`` dtype (:issue:`13663`)

pandas/core/ops.py

@@ -461,7 +461,7 @@ def _convert_to_array(self, values, name=None, other=None):
 
             # a datelike
             elif isinstance(values, pd.DatetimeIndex):
-                values = values.to_series()
+                values = values.to_series(True)
             # datetime with tz
             elif (isinstance(ovalues, datetime.datetime) and
                   hasattr(ovalues, 'tz')):
@@ -543,9 +543,9 @@ def _offset(lvalues, rvalues):
 
                 # with tz, convert to UTC
                 if self.is_datetime64tz_lhs:
-                    lvalues = lvalues.tz_localize(None)
+                    lvalues = lvalues.tz_convert('UTC')
                 if self.is_datetime64tz_rhs:
-                    rvalues = rvalues.tz_localize(None)
+                    rvalues = rvalues.tz_convert('UTC')
 
                 lvalues = lvalues.view(np.int64)
                 rvalues = rvalues.view(np.int64)

pandas/indexes/base.py

@@ -165,7 +165,14 @@ def __new__(cls, data=None, dtype=None, copy=False, name=None,
             if (issubclass(data.dtype.type, np.datetime64) or
                     is_datetimetz(data)):
                 from pandas.tseries.index import DatetimeIndex
-                result = DatetimeIndex(data, copy=copy, name=name, **kwargs)
+                if 'tz' in kwargs:
+                    tz = kwargs['tz']
+                    del kwargs['tz']
+                    result = DatetimeIndex(data, copy=copy, tz='UTC',
+                                           name=name, **kwargs).tz_convert(tz)
+                else:
+                    result = DatetimeIndex(data, copy=copy,
+                                           name=name, **kwargs)
                 if dtype is not None and _o_dtype == dtype:
                     return Index(result.to_pydatetime(), dtype=_o_dtype)
                 else:

pandas/tests/series/test_operators.py

@@ -373,6 +373,17 @@ def test_timedelta64_operations_with_DateOffset(self):
             td - op(5)
             op(5) - td
 
+    def test_timedelta64_operations_with_DatetimeIndex_tz(self):
+        # GH 13905
+        dti = pd.DatetimeIndex(['2016-06-28 05:30', '2016-06-28 05:31'],
+                               dtype='datetime64[ns, America/Chicago]')
+        td = Series(['00:00:05', '00:00:05'], dtype='timedelta64[ns]')
+
+        exp = Series(['2016-06-28 05:30:05-05:00',
+                      '2016-06-28 05:31:05-05:00'],
+                     dtype='datetime64[ns, America/Chicago]')
+        assert_series_equal(dti + td, exp)
+
     def test_timedelta64_operations_with_timedeltas(self):
 
         # td operate with td

pandas/types/cast.py

@@ -820,8 +820,8 @@ def _possibly_cast_to_datetime(value, dtype, errors='raise'):
                             # input has to be UTC at this point, so just
                             # localize
                             value = to_datetime(
-                                value,
-                                errors=errors).tz_localize(dtype.tz)
+                                value, utc=True,
+                                errors=errors).tz_convert(dtype.tz)
                         elif is_timedelta64:
                             value = to_timedelta(value, errors=errors)._values
                     except (AttributeError, ValueError, TypeError):