fixed format errors

Author: raghavendranath

pandas/core/indexes/datetimes.py

@@ -115,12 +115,13 @@ 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.
+    Uses date.fromisoformat() to validate full ISO dates, with fallback to regex
+    for reduced precision dates (YYYY or YYYY-MM) which are not supported by
+    fromisoformat().
 
     Examples of ISO format (True):
-    - 2024
-    - 2024-01
+    - 2024 (reduced precision)
+    - 2024-01 (reduced precision)
     - 2024-01-10
     - 2024-01-10T00:00:00
 
@@ -131,7 +132,19 @@ def _is_iso_format_string(date_str: str) -> bool:
     - 10/01/2024 (DD/MM/YYYY)
     - 01-10-2024 (MM-DD-YYYY)
     """
-    return re.match(r"^\d{4}(?:-|T|$)", date_str) is not None
+    try:
+        # Standard library validates full ISO dates (YYYY-MM-DD format)
+        dt.date.fromisoformat(date_str)
+        return True
+    except (ValueError, TypeError):
+        # Fallback regex for reduced precision dates not supported by fromisoformat()
+        # Checks if string starts with ISO pattern (YYYY, YYYY-MM, YYYY-MM-DD, etc.)
+        # Pattern: ^\d{4}(?:-|T|$)
+        # - Requires exactly 4 digits at start (year)
+        # - Followed by: hyphen (YYYY-), T (YYYY-T...), or end (YYYY)
+        # Examples that match: "2024", "2024-01", "2024-01-10", "2024-01-10T00:00:00"
+        # Examples that don't: "01/10/2024", "2024 01 10", "1/1/2024"
+        return re.match(r"^\d{4}(?:-|T|$)", date_str) is not None
 
 
 @inherit_names(

pandas/tests/indexes/datetimes/test_indexing.py

@@ -489,14 +489,11 @@ 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"])
+        index = DatetimeIndex(["2000-01-03"])
         with pytest.raises(KeyError, match="2000"):
-            index.get_loc("1/1/2000")
+            index.get_loc("2000-01-01")
 
     def test_get_loc_year_str(self):
         rng = date_range("1/1/2000", "1/1/2010")

pandas/tests/indexes/period/test_indexing.py

@@ -172,22 +172,19 @@ 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)
-        pidx = period_range(start="2013/01/01 09:00:00", freq="s", periods=4000)
+        didx = date_range(start="2013-01-01 09:00:00", freq="s", periods=4000)
+        pidx = period_range(start="2013-01-01 09:00:00", freq="s", periods=4000)
 
         for idx in [didx, pidx]:
             # getitem against index should raise ValueError
             values = [
                 "2014",
-                "2013/02",
-                "2013/01/02",
-                "2013/02/01 9h",
-                "2013/02/01 09:00",
+                "2013-02",
+                "2013-01-02",
+                "2013-02-01 9h",
+                "2013-02-01 09:00",
             ]
             for val in values:
                 # GH7116
@@ -197,9 +194,9 @@ def test_getitem_seconds(self):
                     idx[val]
 
             ser = Series(np.random.default_rng(2).random(len(idx)), index=idx)
-            tm.assert_series_equal(ser["2013/01/01 10:00"], ser[3600:3660])
-            tm.assert_series_equal(ser["2013/01/01 9h"], ser[:3600])
-            for d in ["2013/01/01", "2013/01", "2013"]:
+            tm.assert_series_equal(ser["2013-01-01 10:00"], ser[3600:3660])
+            tm.assert_series_equal(ser["2013-01-01 9h"], ser[:3600])
+            for d in ["2013-01-01", "2013-01", "2013"]:
                 tm.assert_series_equal(ser[d], ser)
 
     @pytest.mark.parametrize(