Fix typing and add test + check for NaT

Author: ben-cutler-tamarin

pandas/_libs/tslibs/parsing.pyx

@@ -1071,7 +1071,6 @@ cdef str _fill_token(token: str, padding: int):
     return token_filled
 
 
-
 cpdef str get_rule_month(str source):
     """
     Return starting month of given freq, default is December.

pandas/core/tools/datetimes.py

@@ -1,7 +1,10 @@
 from __future__ import annotations
 
 from collections import abc
-from datetime import date, datetime
+from datetime import (
+    date,
+    datetime,
+)
 from functools import partial
 from itertools import islice
 from typing import (
@@ -29,8 +32,8 @@
     timezones as libtimezones,
 )
 from pandas._libs.tslibs.conversion import cast_from_unit_vectorized
-from pandas._libs.missing import NAType
 from pandas._libs.tslibs.dtypes import NpyDatetimeUnit
+from pandas._libs.tslibs.nattype import NaTType
 from pandas._libs.tslibs.parsing import (
     DateParseError,
     guess_datetime_format,
@@ -84,7 +87,6 @@
         Hashable,
     )
 
-    from pandas._libs.tslibs.nattype import NaTType
     from pandas._libs.tslibs.timedeltas import UnitChoices
 
     from pandas import (
@@ -151,7 +153,7 @@ def _guess_datetime_format_for_array(
             [
                 datetime.strptime(date_string, fmt)
                 for date_string in arr
-                if date_string and not isinstance(date_string, NAType)
+                if date_string and not isinstance(date_string, NaTType)
             ]
             return fmt
         except ValueError:

pandas/tests/tslibs/test_parsing.py

@@ -10,6 +10,7 @@
 import pytest
 
 from pandas._libs.tslibs import (
+    NaT,
     parsing,
     strptime,
 )
@@ -19,7 +20,6 @@
     WASM,
     is_platform_windows,
 )
-from pandas.core.tools.datetimes import _guess_datetime_format_for_array
 import pandas.util._test_decorators as td
 
 # Usually we wouldn't want this import in this test file (which is targeted at
@@ -30,6 +30,7 @@
     option_context,
 )
 import pandas._testing as tm
+from pandas.core.tools.datetimes import _guess_datetime_format_for_array
 
 
 @pytest.mark.skipif(WASM, reason="tzset is not available on WASM")
@@ -453,10 +454,10 @@ def test_parse_datetime_string_with_reso_yearfirst(yearfirst, input):
             np.array(["2025-08-09 14:30:00+0000", "2025-12-01 09:15:00-0500"]),
         ),
         ("%Y-%m-%d", np.array(["2025-08-09", None, "2025-12-01"])),
-        (None, np.array(["2025/13/01", "not-a-date", ""])),
+        (None, np.array(["2025/13/01", "not-a-date", "", NaT])),
         (
             None,
-            np.array(["01/02/2025", "2025-02-01"]),
+            np.array(["01/02/2025", "2025-02-01", np.nan]),
         ),
     ],
 )