BUG: Fix #25959 - Don't call .array in DatetimeLikeArrayMixin's map

doc/source/whatsnew/v0.25.0.rst

@@ -423,6 +423,7 @@ Reshaping
 - Bug in :func:`merge` where merging with equivalent Categorical dtypes was raising an error (:issue:`22501`)
 - bug in :class:`DataFrame` instantiating with a ``range`` (e.g. ``pd.DataFrame(range(3))``) raised an error (:issue:`26342`).
 - Bug in :class:`DataFrame` constructor when passing non-empty tuples would cause a segmentation fault (:issue:`25691`)
+- Bug in :func:`Series.apply` failed when the series is a timezone aware :class:`DatetimeIndex` (:issue:`25959`)
 - Bug in :func:`pandas.cut` where large bins could incorrectly raise an error due to an integer overflow (:issue:`26045`)
 - Bug in :func:`DataFrame.sort_index` where an error is thrown when a multi-indexed DataFrame is sorted on all levels with the initial level sorted last (:issue:`26053`)
 - Bug in :meth:`Series.nlargest` treats ``True`` as smaller than ``False`` (:issue:`26154`)

pandas/core/series.py

@@ -28,6 +28,7 @@
 from pandas.core.dtypes.missing import (
     isna, na_value_for_dtype, notna, remove_na_arraylike)
 
+import pandas as pd
 from pandas.core import algorithms, base, generic, nanops, ops
 from pandas.core.accessor import CachedAccessor
 from pandas.core.arrays import ExtensionArray, SparseArray
@@ -3702,8 +3703,10 @@ def f(x):
                 mapped = lib.map_infer(values, f, convert=convert_dtype)
 
         if len(mapped) and isinstance(mapped[0], Series):
-            from pandas.core.frame import DataFrame
-            return DataFrame(mapped.tolist(), index=self.index)
+            # GH 25959 use pd.array instead of tolist
+            # so extension arrays can be used
+            return self._constructor_expanddim(pd.array(mapped),
+                                               index=self.index)
         else:
             return self._constructor(mapped,
                                      index=self.index).__finalize__(self)

pandas/tests/series/test_apply.py

@@ -671,3 +671,23 @@ def test_map_missing_mixed(self, vals, mapping, exp):
         result = s.map(mapping)
 
         tm.assert_series_equal(result, pd.Series(exp))
+
+    @pytest.mark.parametrize("dti,exp", [
+        (Series([1, 2], index=pd.DatetimeIndex([0, 31536000000])),
+            DataFrame(np.repeat([[1, 2]], 2, axis=0), dtype='int64')),
+        (tm.makeTimeSeries(nper=30),
+            DataFrame(np.repeat([[1, 2]], 30, axis=0), dtype='int64'))
+    ])
+    def test_apply_series_on_date_time_index_aware_series(self, dti, exp):
+        # GH 25959
+        # Calling apply on a localized time series should not cause an error
+        index = dti.tz_localize('UTC').index
+        result = pd.Series(index).apply(lambda x: pd.Series([1, 2]))
+        assert_frame_equal(result, exp)
+
+    def test_apply_scaler_on_date_time_index_aware_series(self):
+        # GH 25959
+        # Calling apply on a localized time series should not cause an error
+        series = tm.makeTimeSeries(nper=30).tz_localize('UTC')
+        result = pd.Series(series.index).apply(lambda x: 1)
+        assert_series_equal(result, pd.Series(np.ones(30), dtype='int64'))