Have DatetimeIndex handle the UTC conversion for Series and reformat tests

Author: mroeschke

pandas/core/tools/datetimes.py

@@ -345,17 +345,6 @@ def to_datetime(arg, errors='raise', dayfirst=False, yearfirst=False,
 
     tz = 'utc' if utc else None
 
-    def _maybe_convert_to_utc(arg, utc):
-        if utc:
-            if isinstance(arg, ABCSeries):
-                arg = arg.dt.tz_localize('UTC')
-            elif isinstance(arg, DatetimeIndex):
-                if arg.tz is None:
-                    arg = arg.tz_localize('UTC')
-                else:
-                    arg = arg.tz_convert('UTC')
-        return arg
-
     def _convert_listlike(arg, box, format, name=None, tz=tz):
 
         if isinstance(arg, (list, tuple)):
@@ -375,7 +364,8 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
                     return DatetimeIndex(arg, tz=tz, name=name)
                 except ValueError:
                     pass
-            arg = _maybe_convert_to_utc(arg, utc)
+
+
             return arg
 
         elif unit is not None:
@@ -394,9 +384,8 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
         elif getattr(arg, 'ndim', 1) > 1:
             raise TypeError('arg must be a string, datetime, list, tuple, '
                             '1-d array, or Series')
-        # _ensure_object converts Series to numpy array, need to reconvert
-        # upon return
-        arg_is_series = isinstance(arg, ABCSeries)
+
+
         arg = _ensure_object(arg)
         require_iso8601 = False
 
@@ -456,9 +445,6 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
                 )
             if is_datetime64_dtype(result) and box:
                 result = DatetimeIndex(result, tz=tz, name=name)
-            # GH 6415
-            elif arg_is_series and utc:
-                result = _maybe_convert_to_utc(Series(result, name=name), utc)
             return result
 
         except ValueError as e:
@@ -533,7 +519,7 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
         result = arg
     elif isinstance(arg, ABCSeries):
         from pandas import Series
-        values = _convert_listlike(arg, False, format, name=arg.name)
+        values = _convert_listlike(arg, True, format)
         result = Series(values, index=arg.index, name=arg.name)
     elif isinstance(arg, (ABCDataFrame, MutableMapping)):
         result = _assemble_from_unit_mappings(arg, errors=errors)

pandas/tests/indexes/datetimes/test_tools.py

@@ -269,37 +269,39 @@ def test_to_datetime_utc_is_true(self):
         result = pd.to_datetime(date_range, utc=True)
         expected = pd.DatetimeIndex(data=date_range)
         tm.assert_index_equal(result, expected)
-
-    def test_to_datetime_utc_true_with_series(self):
+    
+    @pytest.mark.parametrize("init_constructor, end_constructor, test_method",
+        [(Index, DatetimeIndex, tm.assert_index_equal),
+         (Series, Series, tm.assert_series_equal)])
+    def test_to_datetime_utc_true_with_series(self, 
+                                              init_constructor, 
+                                              end_constructor, 
+                                              test_method):
         # GH 6415: UTC=True with Series
         data = ['20100102 121314', '20100102 121315']
         expected_data = [pd.Timestamp('2010-01-02 12:13:14', tz='utc'),
                          pd.Timestamp('2010-01-02 12:13:15', tz='utc')]
-        result = pd.to_datetime(pd.Series(data),
-                                format='%Y%m%d %H%M%S',
-                                utc=True)
-        expected = pd.Series(expected_data)
-        tm.assert_series_equal(result, expected)
-        result = pd.to_datetime(pd.Index(data),
+
+        result = pd.to_datetime(init_constructor(data),
                                 format='%Y%m%d %H%M%S',
                                 utc=True)
-        expected = pd.DatetimeIndex(expected_data)
-        tm.assert_index_equal(result, expected)
+        expected = end_constructor(expected_data)
+        test_method(result, expected)
 
+    def test_to_datetime_utc_true_with_series_single_value(self):
         # GH 15760 UTC=True with Series
         ts = 1.5e18
         result = pd.to_datetime(pd.Series([ts]), utc=True)
         expected = pd.Series([pd.Timestamp(ts, tz='utc')])
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize("dtype", [None, 'datetime64[ns]'])
+    def test_to_datetime_utc_true_with_naive_series(self, dtype):
         test_dates = ['2013-01-01 00:00:00-01:00'] * 10
+        ser = pd.Series(test_dates, dtype=dtype)
+        result = pd.to_datetime(ser, utc=True)
         expected_data = [pd.Timestamp('20130101 01:00:00', tz='utc')] * 10
         expected = pd.Series(expected_data)
-        ser = Series(test_dates)
-        result = pd.to_datetime(ser, utc=True)
-        tm.assert_series_equal(result, expected)
-        ser_naive = Series(test_dates, dtype='datetime64[ns]')
-        result = pd.to_datetime(ser_naive, utc=True)
         tm.assert_series_equal(result, expected)
 
     def test_to_datetime_tz_psycopg2(self):