Refactor: Move non-ISO date format deprecation to .loc-specific path due to other test failures

Author: raghavendranath

pandas/core/indexes/datetimes.py

@@ -2,7 +2,6 @@
 
 import datetime as dt
 import operator
-import re
 from typing import (
     TYPE_CHECKING,
     Self,
@@ -111,29 +110,6 @@ def _new_DatetimeIndex(cls, d):
     return result
 
 
-def _is_iso_format_string(date_str: str) -> bool:
-    """
-    Check if a date string follows ISO8601 format.
-
-    ISO format must start with a 4-digit year (YYYY), optionally followed by
-    hyphen-separated month and day or 'T' for time component.
-
-    Examples of ISO format (True):
-    - 2024
-    - 2024-01
-    - 2024-01-10
-    - 2024-01-10T00:00:00
-
-    Examples of non-ISO format (False):
-    - 2024/01/10 (/ separator)
-    - 2024 01 10 (space separator)
-    - 01/10/2024 (MM/DD/YYYY)
-    - 10/01/2024 (DD/MM/YYYY)
-    - 01-10-2024 (MM-DD-YYYY)
-    """
-    return re.match(r"^\d{4}(?:-|T|$)", date_str) is not None
-
-
 @inherit_names(
     DatetimeArray._field_ops
     + [
@@ -637,14 +613,6 @@ def get_loc(self, key):
                 parsed, reso = self._parse_with_reso(key)
             except ValueError as err:
                 raise KeyError(key) from err
-            # GH#58302 - Deprecate non-ISO string formats in .loc indexing
-            if not _is_iso_format_string(key):
-                msg = (
-                    "Parsing non-ISO datetime strings in .loc is deprecated "
-                    "and will be removed in a future version. Use ISO format "
-                    f"(YYYY-MM-DD) instead. Got '{key}'."
-                )
-                warnings.warn(msg, Pandas4Warning, stacklevel=find_stack_level())
             self._disallow_mismatched_indexing(parsed)
 
             if self._can_partial_date_slice(reso):
@@ -720,23 +688,6 @@ def slice_indexer(self, start=None, end=None, step=None):
         def check_str_or_none(point) -> bool:
             return point is not None and not isinstance(point, str)
 
-        # GH#58302 - Deprecate non-ISO string formats in .loc indexing
-        if isinstance(start, str) and not _is_iso_format_string(start):
-            msg = (
-                "Parsing non-ISO datetime strings in .loc is deprecated "
-                "and will be removed in a future version. Use ISO format "
-                f"(YYYY-MM-DD) instead. Got '{start}'."
-            )
-            warnings.warn(msg, Pandas4Warning, stacklevel=find_stack_level())
-
-        if isinstance(end, str) and not _is_iso_format_string(end):
-            msg = (
-                "Parsing non-ISO datetime strings in .loc is deprecated "
-                "and will be removed in a future version. Use ISO format "
-                f"(YYYY-MM-DD) instead. Got '{end}'."
-            )
-            warnings.warn(msg, Pandas4Warning, stacklevel=find_stack_level())
-
         # GH#33146 if start and end are combinations of str and None and Index is not
         # monotonic, we can not use Index.slice_indexer because it does not honor the
         # actual elements, is only searching for start and end
@@ -756,7 +707,6 @@ def check_str_or_none(point) -> bool:
 
         if end is not None:
             end_casted = self._maybe_cast_slice_bound(end, "right")
-
             mask = (self <= end_casted) & mask
             in_index &= (end_casted == self).any()
 

pandas/core/indexing.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from contextlib import suppress
+import re
 import sys
 from typing import (
     TYPE_CHECKING,
@@ -26,11 +27,13 @@
     IndexingError,
     InvalidIndexError,
     LossySetitemError,
+    Pandas4Warning,
 )
 from pandas.errors.cow import _chained_assignment_msg
 from pandas.util._decorators import (
     doc,
 )
+from pandas.util._exceptions import find_stack_level
 
 from pandas.core.dtypes.cast import (
     can_hold_element,
@@ -1249,6 +1252,31 @@ class _LocIndexer(_LocationIndexer):
         "index is integers), listlike of labels, boolean"
     )
 
+    # -------------------------------------------------------------------
+    # Helpers
+
+    @staticmethod
+    def _is_iso_format_string(date_str: str) -> bool:
+        """
+        Check if a date string follows ISO 8601 format.
+
+        ISO format must start with a 4-digit year (YYYY), optionally followed by
+        hyphen or 'T' for time component.
+
+        Examples of ISO format (True):
+        - "2024"
+        - "2024-01"
+        - "2024-01-10"
+        - "2024-01-10T00:00:00"
+
+        Examples of non-ISO format (False):
+        - "2024/01/10" (/ separator)
+        - "2024 01 10" (space separator)
+        - "01/10/2024" (MM/DD/YYYY)
+        - "1Q01" (quarter format)
+        """
+        return re.match(r"^\d{4}(?:-|T|$)", date_str) is not None
+
     # -------------------------------------------------------------------
     # Key Checks
 
@@ -1459,6 +1487,19 @@ def _getitem_axis(self, key, axis: AxisInt):
 
         # fall thru to straight lookup
         self._validate_key(key, axis)
+
+        # GH#58302 - Deprecate non-ISO string formats in .loc direct access
+        # Only warn for DatetimeIndex to avoid false positives with other index types
+        labels = self.obj._get_axis(axis)
+        if type(labels).__name__ == "DatetimeIndex":
+            if isinstance(key, str) and not self._is_iso_format_string(key):
+                msg = (
+                    "Parsing non-ISO datetime strings in .loc is deprecated "
+                    "and will be removed in a future version. Use ISO format "
+                    f"(YYYY-MM-DD) instead. Got '{key}'."
+                )
+                warnings.warn(msg, Pandas4Warning, stacklevel=find_stack_level())
+
         return self._get_label(key, axis=axis)
 
     def _get_slice_axis(self, slice_obj: slice, axis: AxisInt):
@@ -1471,6 +1512,19 @@ def _get_slice_axis(self, slice_obj: slice, axis: AxisInt):
             return obj.copy(deep=False)
 
         labels = obj._get_axis(axis)
+
+        # GH#58302 - Deprecate non-ISO string formats in .loc slicing
+        # Only warn for DatetimeIndex to avoid false positives with other index types
+        if type(labels).__name__ == "DatetimeIndex":
+            for key in [slice_obj.start, slice_obj.stop]:
+                if isinstance(key, str) and not self._is_iso_format_string(key):
+                    msg = (
+                        "Parsing non-ISO datetime strings in .loc is deprecated "
+                        "and will be removed in a future version. Use ISO format "
+                        f"(YYYY-MM-DD) instead. Got '{key}'."
+                    )
+                    warnings.warn(msg, Pandas4Warning, stacklevel=find_stack_level())
+
         indexer = labels.slice_indexer(slice_obj.start, slice_obj.stop, slice_obj.step)
 
         if isinstance(indexer, slice):

pandas/tests/groupby/test_groupby.py

@@ -2851,9 +2851,6 @@ def test_groupby_with_Time_Grouper(unit):
     tm.assert_frame_equal(result, expected_output)
 
 
-@pytest.mark.filterwarnings(
-    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
-)
 def test_groupby_series_with_datetimeindex_month_name():
     # GH 48509
     s = Series([0, 1, 0], index=date_range("2022-01-01", periods=3), name="jan")

pandas/tests/indexes/datetimes/test_partial_slicing.py

@@ -21,10 +21,9 @@
 
 
 class TestSlicing:
-    pytestmark = pytest.mark.filterwarnings(
+    @pytest.mark.filterwarnings(
         "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
     )
-
     def test_string_index_series_name_converted(self):
         # GH#1644
         df = DataFrame(
@@ -159,6 +158,9 @@ def test_slice_end_of_period_resolution(self, partial_dtime):
         expected = ser.iloc[:5]
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.filterwarnings(
+        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+    )
     def test_slice_quarter(self):
         dti = date_range(freq="D", start=datetime(2000, 6, 1), periods=500)
 

pandas/tests/indexes/period/test_partial_slicing.py

@@ -12,10 +12,6 @@
 
 
 class TestPeriodIndex:
-    pytestmark = pytest.mark.filterwarnings(
-        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
-    )
-
     def test_getitem_periodindex_duplicates_string_slice(self):
         # monotonic
         idx = PeriodIndex([2000, 2007, 2007, 2009, 2009], freq="Y-JUN")
@@ -127,6 +123,9 @@ def test_range_slice_outofbounds(self, make_range):
         tm.assert_frame_equal(df["2013-11":"2013-12"], empty)
 
     @pytest.mark.parametrize("make_range", [date_range, period_range])
+    @pytest.mark.filterwarnings(
+        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+    )
     def test_maybe_cast_slice_bound(self, make_range, frame_or_series):
         idx = make_range(start="2013/10/01", freq="D", periods=10)
 

pandas/tests/series/indexing/test_getitem.py

@@ -236,9 +236,6 @@ def test_getitem_partial_str_slice_with_datetimeindex(self):
 
         tm.assert_series_equal(result, expected)
 
-    @pytest.mark.filterwarnings(
-        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
-    )
     def test_getitem_slice_strings_with_datetimeindex(self):
         idx = DatetimeIndex(
             ["1/1/2000", "1/2/2000", "1/2/2000", "1/3/2000", "1/4/2000"]