BUG: preserve object-dtype index when accessing DataFrame column / PERF: improve perf of Series fastpath constructor

doc/source/whatsnew/v1.4.0.rst

@@ -698,6 +698,7 @@ Indexing
 - Bug in indexing on columns with ``loc`` or ``iloc`` using a slice with a negative step with ``ExtensionDtype`` columns incorrectly raising (:issue:`44551`)
 - Bug in :meth:`IntervalIndex.get_indexer_non_unique` returning boolean mask instead of array of integers for a non unique and non monotonic index (:issue:`44084`)
 - Bug in :meth:`IntervalIndex.get_indexer_non_unique` not handling targets of ``dtype`` 'object' with NaNs correctly (:issue:`44482`)
+- Bug in getting a column from a DataFrame with an object-dtype row index with datetime-like values: the resulting Series now preserves the exact object-dtype Index from the parent DataFrame (:issue:`42950`)
 -
 
 Missing

pandas/tests/frame/indexing/test_indexing.py

@@ -1526,3 +1526,18 @@ def test_loc_iloc_setitem_non_categorical_rhs(
         # "c" not part of the categories
         with pytest.raises(TypeError, match=msg1):
             indexer(df)[key] = ["c", "c"]
+
+    @pytest.mark.parametrize("indexer", [tm.getitem, tm.loc, tm.iloc])
+    def test_getitem_preserve_object_index_with_dates(self, indexer):
+        # https://github.com/pandas-dev/pandas/pull/42950 - when selecting a column
+        # from dataframe, don't try to infer object dtype index on Series construction
+        idx = date_range("2012", periods=3).astype(object)
+        df = DataFrame({0: [1, 2, 3]}, index=idx)
+        assert df.index.dtype == object
+
+        if indexer is tm.getitem:
+            ser = indexer(df)[0]
+        else:
+            ser = indexer(df)[:, 0]
+
+        assert ser.index.dtype == object