Fix: Ensure non-ISO deprecation warnings trigger in slice_indexer and add test suppressions

Author: raghavendranath

pandas/core/indexes/datetimes.py

@@ -116,21 +116,22 @@ 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
-    month and day with consistent separators.
+    hyphen-separated month and day or 'T' for time component.
 
     Examples of ISO format (True):
+    - 2024
+    - 2024-01
     - 2024-01-10
-    - 2024/01/10
-    - 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)
     """
-    # ISO format must start with 4-digit year followed by separator (-, /, ., or space)
-    return re.match(r"^\d{4}[-/. ]", date_str) is not None
+    return re.match(r"^\d{4}(?:-|T|$)", date_str) is not None
 
 
 @inherit_names(
@@ -722,6 +723,23 @@ def check_str_or_none(point) -> bool:
         # 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
+        # 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())
+
         if (
             check_str_or_none(start)
             or check_str_or_none(end)
@@ -733,31 +751,12 @@ def check_str_or_none(point) -> bool:
         in_index = True
         if start is not None:
             start_casted = self._maybe_cast_slice_bound(start, "left")
-
-            # 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())
-
             mask = start_casted <= self
             in_index &= (start_casted == self).any()
 
         if end is not None:
             end_casted = self._maybe_cast_slice_bound(end, "right")
 
-            # GH#58302 - Deprecate non-ISO string formats in .loc indexing
-            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())
-
             mask = (self <= end_casted) & mask
             in_index &= (end_casted == self).any()
 

pandas/tests/groupby/test_groupby.py

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

pandas/tests/indexes/datetimes/test_indexing.py

@@ -26,10 +26,6 @@
 
 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)
 
 
@@ -493,6 +489,9 @@ def test_get_loc_timedelta_invalid_key(self, key):
         with pytest.raises(TypeError, match=msg):
             dti.get_loc(key)
 
+    @pytest.mark.filterwarnings(
+        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+    )
     def test_get_loc_reasonable_key_error(self):
         # GH#1062
         index = DatetimeIndex(["1/3/2000"])

pandas/tests/indexes/datetimes/test_partial_slicing.py

@@ -501,13 +501,11 @@ def test_loc_indexing_non_iso_single_key_deprecation(self, ser_daily, date_strin
     @pytest.mark.parametrize(
         "date_string,expected",
         [
-            ("2024-01-10", 9),  # YYYY-MM-DD (dash)
-            ("2024/01/10", 9),  # YYYY/MM/DD (slash)
-            ("2024 01 10", 9),  # YYYY MM DD (space)
+            ("2024-01-10", 9),  # YYYY-MM-DD (ISO format)
         ],
     )
     def test_loc_indexing_iso_format_no_warning(self, ser_daily, date_string, expected):
-        # GH#58302 - ISO formats should NOT warn
+        # GH#58302 - ISO format (YYYY-MM-DD) should NOT warn
         with tm.assert_produces_warning(None):
             result = ser_daily.loc[date_string]
             assert result == expected

pandas/tests/indexes/multi/test_partial_indexing.py

@@ -9,10 +9,6 @@
 )
 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

@@ -21,10 +21,6 @@
 )
 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))
@@ -176,6 +172,9 @@ def test_getitem_list_periods(self):
         tm.assert_series_equal(ts[[Period("2012-01-02", freq="D")]], exp)
 
     @pytest.mark.arm_slow
+    @pytest.mark.filterwarnings(
+        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+    )
     def test_getitem_seconds(self):
         # GH#6716
         didx = date_range(start="2013/01/01 09:00:00", freq="s", periods=4000)
@@ -210,6 +209,9 @@ def test_getitem_seconds(self):
             period_range,
         ],
     )
+    @pytest.mark.filterwarnings(
+        "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+    )
     def test_getitem_day(self, idx_range):
         # GH#6716
         # Confirm DatetimeIndex and PeriodIndex works identically

pandas/tests/indexes/period/test_partial_slicing.py

@@ -10,12 +10,12 @@
 )
 import pandas._testing as tm
 
-pytestmark = pytest.mark.filterwarnings(
-    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
-)
-
 
 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")

pandas/tests/indexing/multiindex/test_slice.py

@@ -19,10 +19,6 @@
 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

@@ -44,10 +44,6 @@
 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

@@ -38,10 +38,6 @@
 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():
@@ -331,6 +327,9 @@ def test_resample_rounding(unit):
     tm.assert_frame_equal(result, expected)
 
 
+@pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
 def test_resample_basic_from_daily(unit):
     # from daily
     dti = date_range(
@@ -555,6 +554,9 @@ def test_resample_ohlc(unit):
     assert xs["close"] == s.iloc[4]
 
 
+@pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
 def test_resample_ohlc_result(unit):
     # GH 12332
     index = date_range("1-1-2000", "2-15-2000", freq="h").as_unit(unit)
@@ -666,6 +668,9 @@ def test_resample_timestamp_to_period(
     tm.assert_series_equal(result, expected)
 
 
+@pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
 def test_ohlc_5min(unit):
     def _ohlc(group):
         if isna(group).all():
@@ -1580,6 +1585,9 @@ def test_resample_dst_anchor(unit):
     )
 
 
+@pytest.mark.filterwarnings(
+    "ignore:Parsing non-ISO datetime strings:pandas.errors.Pandas4Warning"
+)
 def test_resample_dst_anchor2(unit):
     dti = date_range(
         "2013-09-30", "2013-11-02", freq="30Min", tz="Europe/Paris"