fix: only warn on non-ISO formats in .loc indexing paths

Author: raghavendranath

pandas/core/indexes/datetimes.py

@@ -591,15 +591,6 @@ def _parsed_string_to_bounds(
     def _parse_with_reso(self, label: str) -> tuple[Timestamp, Resolution]:
         parsed, reso = super()._parse_with_reso(label)
 
-        # GH#58302 - Deprecate non-ISO string formats in .loc indexing
-        if isinstance(label, str) and not _is_iso_format_string(label):
-            msg = (
-                "Parsing non-ISO datetime strings in .loc is deprecated and will be "
-                "removed in a future version. Use ISO format (YYYY-MM-DD) instead. "
-                f"Got '{label}'."
-            )
-            warnings.warn(msg, Pandas4Warning, stacklevel=find_stack_level())
-
         parsed = Timestamp(parsed)
 
         if self.tz is not None and parsed.tzinfo is None:
@@ -645,6 +636,14 @@ 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):

pandas/tests/groupby/test_groupby.py

@@ -28,7 +28,12 @@
 from pandas.core.arrays import BooleanArray
 import pandas.core.common as com
 
-pytestmark = pytest.mark.filterwarnings("ignore:Mean of empty slice:RuntimeWarning")
+pytestmark = [
+    pytest.mark.filterwarnings("ignore:Mean of empty slice:RuntimeWarning"),
+    pytest.mark.filterwarnings(
+        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+    ),
+]
 
 
 def test_repr():

pandas/tests/indexes/datetimes/test_indexing.py

@@ -26,6 +26,10 @@
 
 from pandas.tseries.frequencies import to_offset
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 START, END = datetime(2009, 1, 1), datetime(2010, 1, 1)
 
 

pandas/tests/indexes/datetimes/test_partial_slicing.py

@@ -19,6 +19,10 @@
 )
 import pandas._testing as tm
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 
 class TestSlicing:
     def test_string_index_series_name_converted(self):

pandas/tests/indexes/multi/test_partial_indexing.py

@@ -9,6 +9,10 @@
 )
 import pandas._testing as tm
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 
 @pytest.fixture
 def df():

pandas/tests/indexes/period/test_indexing.py

@@ -21,6 +21,10 @@
 )
 import pandas._testing as tm
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 dti4 = date_range("2016-01-01", periods=4)
 dti = dti4[:-1]
 rng = pd.Index(range(3))

pandas/tests/indexes/period/test_partial_slicing.py

@@ -10,6 +10,10 @@
 )
 import pandas._testing as tm
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 
 class TestPeriodIndex:
     def test_getitem_periodindex_duplicates_string_slice(self):

pandas/tests/indexing/multiindex/test_slice.py

@@ -19,6 +19,10 @@
 import pandas._testing as tm
 from pandas.tests.indexing.common import _mklbl
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 
 class TestMultiIndexSlicers:
     def test_per_axis_per_level_getitem(self):

pandas/tests/indexing/test_loc.py

@@ -44,6 +44,10 @@
 from pandas.core.indexing import _one_ellipsis_message
 from pandas.tests.indexing.common import check_indexing_smoketest_or_raises
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 
 @pytest.mark.parametrize(
     "series, new_series, expected_ser",

pandas/tests/resample/test_datetime_index.py

@@ -38,6 +38,10 @@
 from pandas.tseries.frequencies import to_offset
 from pandas.tseries.offsets import Minute
 
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
+
 
 @pytest.fixture
 def simple_date_range_series():