BUG: Remove special-casing for date objects in DatetimeIndex indexing (GH#62158)

doc/source/whatsnew/v3.0.0.rst

@@ -889,6 +889,8 @@ Datetimelike
 - Bug in constructing arrays with :class:`ArrowDtype` with ``timestamp`` type incorrectly allowing ``Decimal("NaN")`` (:issue:`61773`)
 - Bug in constructing arrays with a timezone-aware :class:`ArrowDtype` from timezone-naive datetime objects incorrectly treating those as UTC times instead of wall times like :class:`DatetimeTZDtype` (:issue:`61775`)
 - Bug in setting scalar values with mismatched resolution into arrays with non-nanosecond ``datetime64``, ``timedelta64`` or :class:`DatetimeTZDtype` incorrectly truncating those scalars (:issue:`56410`)
+- Removed the special casing for sequences of Python ``date`` objects in ``DatetimeIndex.get_indexer`` and related indexing logic.
+  Indexing a ``DatetimeIndex`` with Python ``date`` objects now behaves consistently with other types. (:issue:`62158`)
 
 Timedelta
 ^^^^^^^^^

pandas/core/indexes/base.py

@@ -39,7 +39,6 @@
     no_default,
 )
 from pandas._libs.tslibs import (
-    OutOfBoundsDatetime,
     Timestamp,
     tz_compare,
 )
@@ -6204,11 +6203,6 @@ def _maybe_downcast_for_indexing(self, other: Index) -> tuple[Index, Index]:
                 # standardize on UTC
                 return self.tz_convert("UTC"), other.tz_convert("UTC")
 
-        elif self.inferred_type == "date" and isinstance(other, ABCDatetimeIndex):
-            try:
-                return type(other)(self), other
-            except OutOfBoundsDatetime:
-                return self, other
         elif self.inferred_type == "timedelta" and isinstance(other, ABCTimedeltaIndex):
             # TODO: we dont have tests that get here
             return type(other)(self), other

pandas/tests/frame/indexing/test_indexing.py

@@ -1880,6 +1880,30 @@ def test_add_new_column_infer_string():
     tm.assert_frame_equal(df, expected)
 
 
+def test_datetime_indexer_consistency_pyarrow_date32():
+    # GH#62158
+    pytest.importorskip("pyarrow", minversion="13.0.0")
+    import pyarrow as pa
+
+    ser = Series(["2016-01-01"], dtype="date32[pyarrow]")
+    ser3 = ser.astype("datetime64[ns]")
+    dti = Index(ser3)
+
+    # Make sure we don't treat Arrow date as timestamp
+    dtype = ser.dtype.pyarrow_dtype
+    assert not (pa.types.is_timestamp(dtype) and not pa.types.is_date(dtype))
+
+    with pytest.raises(KeyError):
+        dti.get_loc(ser[0])
+
+    # get_indexer returns -1 for both Arrow array and object-cast
+    result = dti.get_indexer(ser.values)
+    tm.assert_numpy_array_equal(result, np.array([-1], dtype=np.intp))
+
+    result_obj = dti.get_indexer(ser.values.astype(object))
+    tm.assert_numpy_array_equal(result_obj, np.array([-1], dtype=np.intp))
+
+
 class TestSetitemValidation:
     # This is adapted from pandas/tests/arrays/masked/test_indexing.py
     def _check_setitem_invalid(self, df, invalid, indexer):

pandas/tests/frame/methods/test_asfreq.py

@@ -192,9 +192,10 @@ def test_asfreq_with_date_object_index(self, frame_or_series):
         ts2 = ts.copy()
         ts2.index = [x.date() for x in ts2.index]
 
-        result = ts2.asfreq("4h", method="ffill")
-        expected = ts.asfreq("4h", method="ffill")
-        tm.assert_equal(result, expected)
+        with pytest.raises(
+            TypeError, match="Cannot compare Timestamp with datetime.date"
+        ):
+            ts2.asfreq("4h", method="ffill")
 
     def test_asfreq_with_unsorted_index(self, frame_or_series):
         # GH#39805

pandas/tests/indexes/datetimes/test_indexing.py

@@ -514,10 +514,11 @@ def test_contains_nonunique(self, vals):
 
 class TestGetIndexer:
     def test_get_indexer_date_objs(self):
+        # Behavior for get_indexer with date objects changed in GH#62158.
         rng = date_range("1/1/2000", periods=20)
 
         result = rng.get_indexer(rng.map(lambda x: x.date()))
-        expected = rng.get_indexer(rng)
+        expected = np.full(len(rng), -1, dtype=np.intp)
         tm.assert_numpy_array_equal(result, expected)
 
     def test_get_indexer(self):
@@ -562,17 +563,22 @@ def test_get_indexer(self):
             idx.get_indexer(idx[[0]], method="nearest", tolerance="foo")
 
     @pytest.mark.parametrize(
-        "target",
+        "target, expected",
         [
-            [date(2020, 1, 1), Timestamp("2020-01-02")],
-            [Timestamp("2020-01-01"), date(2020, 1, 2)],
+            (
+                [date(2020, 1, 1), Timestamp("2020-01-02")],
+                np.array([-1, 1], dtype=np.intp),
+            ),
+            (
+                [Timestamp("2020-01-01"), Timestamp(date(2020, 1, 2))],
+                np.array([0, 1], dtype=np.intp),
+            ),
         ],
     )
-    def test_get_indexer_mixed_dtypes(self, target):
+    def test_get_indexer_mixed_dtypes(self, target, expected):
         # https://github.com/pandas-dev/pandas/issues/33741
         values = DatetimeIndex([Timestamp("2020-01-01"), Timestamp("2020-01-02")])
         result = values.get_indexer(target)
-        expected = np.array([0, 1], dtype=np.intp)
         tm.assert_numpy_array_equal(result, expected)
 
     @pytest.mark.parametrize(

pandas/tests/series/test_arithmetic.py

@@ -758,6 +758,8 @@ def test_datetime_understood(self, unit):
         tm.assert_series_equal(result, expected)
 
     def test_align_date_objects_with_datetimeindex(self):
+        # GH#62158: v3.0.0 - DatetimeIndex no longer matches Python date labels.
+        # The result is always all-NaN and the union index.
         rng = date_range("1/1/2000", periods=20)
         ts = Series(np.random.default_rng(2).standard_normal(20), index=rng)
 
@@ -767,10 +769,22 @@ def test_align_date_objects_with_datetimeindex(self):
 
         result = ts + ts2
         result2 = ts2 + ts
-        expected = ts + ts[5:]
-        expected.index = expected.index._with_freq(None)
-        tm.assert_series_equal(result, expected)
-        tm.assert_series_equal(result2, expected)
+
+        date_labels = [x.date() for x in rng[5:]]
+        expected_index_result = Index(list(rng) + date_labels, dtype=object)
+        expected_index_result2 = Index(date_labels + list(rng), dtype=object)
+
+        # Length and index checks
+        assert len(result) == 35
+        tm.assert_index_equal(result.index, expected_index_result)
+        tm.assert_index_equal(result2.index, expected_index_result2)
+        assert result.index.dtype == object
+
+        # All NaN because there are no matching labels now
+        assert result.isna().all()
+        assert result2.isna().all()
+
+        tm.assert_series_equal(result, result2)
 
 
 class TestNamePreservation: