Backport PR #47547 on branch 1.4.x (REGR: NotImplementedError: Prefix not defined when slicing offset with loc)

doc/source/whatsnew/v1.4.4.rst

@@ -22,6 +22,7 @@ Fixed regressions
 - Fixed regression in :meth:`DataFrame.loc` not updating the cache correctly after values were set (:issue:`47867`)
 - Fixed regression in :meth:`DataFrame.loc` not aligning index in some cases when setting a :class:`DataFrame` (:issue:`47578`)
 - Fixed regression in :meth:`DataFrame.loc` setting a length-1 array like value to a single value in the DataFrame (:issue:`46268`)
+- Fixed regression when slicing with :meth:`DataFrame.loc` with :class:`DateOffset`-index (:issue:`46671`)
 - Fixed regression in setting ``None`` or non-string value into a ``string``-dtype Series using a mask (:issue:`47628`)
 - Fixed regression using custom Index subclasses (for example, used in xarray) with :meth:`~DataFrame.reset_index` or :meth:`Index.insert` (:issue:`47071`)
 - Fixed regression in :meth:`DatetimeIndex.intersection` when the :class:`DatetimeIndex` has dates crossing daylight savings time (:issue:`46702`)

pandas/core/indexes/datetimelike.py

@@ -228,7 +228,12 @@ def _parsed_string_to_bounds(self, reso: Resolution, parsed):
 
     def _parse_with_reso(self, label: str):
         # overridden by TimedeltaIndex
-        parsed, reso_str = parsing.parse_time_string(label, self.freq)
+        try:
+            if self.freq is None or hasattr(self.freq, "rule_code"):
+                freq = self.freq
+        except NotImplementedError:
+            freq = getattr(self, "freqstr", getattr(self, "inferred_freq", None))
+        parsed, reso_str = parsing.parse_time_string(label, freq)
         reso = Resolution.from_attrname(reso_str)
         return parsed, reso
 

pandas/tests/frame/indexing/test_getitem.py

@@ -8,12 +8,14 @@
     CategoricalDtype,
     CategoricalIndex,
     DataFrame,
+    DateOffset,
     DatetimeIndex,
     Index,
     MultiIndex,
     Series,
     Timestamp,
     concat,
+    date_range,
     get_dummies,
     period_range,
 )
@@ -165,6 +167,47 @@ def test_getitem_iloc_two_dimensional_generator(self):
         expected = Series([5, 6], name="b", index=[1, 2])
         tm.assert_series_equal(result, expected)
 
+    def test_getitem_iloc_dateoffset_days(self):
+        # GH 46671
+        df = DataFrame(
+            list(range(10)),
+            index=date_range("01-01-2022", periods=10, freq=DateOffset(days=1)),
+        )
+        result = df.loc["2022-01-01":"2022-01-03"]
+        expected = DataFrame(
+            [0, 1, 2],
+            index=DatetimeIndex(
+                ["2022-01-01", "2022-01-02", "2022-01-03"],
+                dtype="datetime64[ns]",
+                freq=DateOffset(days=1),
+            ),
+        )
+        tm.assert_frame_equal(result, expected)
+
+        df = DataFrame(
+            list(range(10)),
+            index=date_range(
+                "01-01-2022", periods=10, freq=DateOffset(days=1, hours=2)
+            ),
+        )
+        result = df.loc["2022-01-01":"2022-01-03"]
+        expected = DataFrame(
+            [0, 1, 2],
+            index=DatetimeIndex(
+                ["2022-01-01 00:00:00", "2022-01-02 02:00:00", "2022-01-03 04:00:00"],
+                dtype="datetime64[ns]",
+                freq=DateOffset(days=1, hours=2),
+            ),
+        )
+        tm.assert_frame_equal(result, expected)
+
+        df = DataFrame(
+            list(range(10)),
+            index=date_range("01-01-2022", periods=10, freq=DateOffset(minutes=3)),
+        )
+        result = df.loc["2022-01-01":"2022-01-03"]
+        tm.assert_frame_equal(result, df)
+
 
 class TestGetitemCallable:
     def test_getitem_callable(self, float_frame):