move format_is_iso to strptime

Author: MarcoGorelli

pandas/_libs/tslibs/parsing.pyi

@@ -40,7 +40,6 @@ def try_parse_datetime_components(
     minutes: npt.NDArray[np.object_],  # object[:]
     seconds: npt.NDArray[np.object_],  # object[:]
 ) -> npt.NDArray[np.object_]: ...
-def format_is_iso(f: str) -> bool: ...
 def guess_datetime_format(
     dt_str,
     dayfirst: bool | None = ...,

pandas/_libs/tslibs/parsing.pyx

@@ -839,26 +839,6 @@ class _timelex:
 _DATEUTIL_LEXER_SPLIT = _timelex.split
 
 
-def format_is_iso(f: str) -> bint:
-    """
-    Does format match the iso8601 set that can be handled by the C parser?
-    Generally of form YYYY-MM-DDTHH:MM:SS - date separator can be different
-    but must be consistent.  Leading 0s in dates and times are optional.
-    """
-    iso_template = "%Y{date_sep}%m{date_sep}%d{time_sep}%H:%M:%S{micro_or_tz}".format
-    excluded_formats = ["%Y%m"]
-
-    for date_sep in [" ", "/", "\\", "-", ".", ""]:
-        for time_sep in [" ", "T"]:
-            for micro_or_tz in ["", "%z", ".%f", ".%f%z"]:
-                if (iso_template(date_sep=date_sep,
-                                 time_sep=time_sep,
-                                 micro_or_tz=micro_or_tz,
-                                 ).startswith(f) and f not in excluded_formats):
-                    return True
-    return False
-
-
 def guess_datetime_format(dt_str: str, bint dayfirst=False) -> str | None:
     """
     Guess the datetime format of a given datetime string.

pandas/_libs/tslibs/strptime.pxd

@@ -1,4 +1,5 @@
 from numpy cimport int64_t
 
 
+cpdef bint format_is_iso(str f)
 cdef bint parse_today_now(str val, int64_t* iresult, bint utc)

pandas/_libs/tslibs/strptime.pyx

@@ -53,6 +53,26 @@ from pandas._libs.tslibs.timestamps import Timestamp
 
 cnp.import_array()
 
+cpdef bint format_is_iso(f: str):
+    """
+    Does format match the iso8601 set that can be handled by the C parser?
+    Generally of form YYYY-MM-DDTHH:MM:SS - date separator can be different
+    but must be consistent.  Leading 0s in dates and times are optional.
+    """
+    iso_template = "%Y{date_sep}%m{date_sep}%d{time_sep}%H:%M:%S{micro_or_tz}".format
+    excluded_formats = ["%Y%m"]
+
+    for date_sep in [" ", "/", "\\", "-", ".", ""]:
+        for time_sep in [" ", "T"]:
+            for micro_or_tz in ["", "%z", ".%f", ".%f%z"]:
+                if (iso_template(date_sep=date_sep,
+                                 time_sep=time_sep,
+                                 micro_or_tz=micro_or_tz,
+                                 ).startswith(f) and f not in excluded_formats):
+                    return True
+    return False
+
+
 cdef bint parse_today_now(str val, int64_t* iresult, bint utc):
     # We delay this check for as long as possible
     # because it catches relatively rare cases
@@ -114,8 +134,6 @@ def array_strptime(
     exact : matches must be exact if True, search if False
     errors : string specifying error handling, {'raise', 'ignore', 'coerce'}
     """
-    from pandas._libs.tslibs.parsing import format_is_iso
-
     cdef:
         Py_ssize_t i, n = len(values)
         npy_datetimestruct dts

pandas/tests/tslibs/test_parsing.py

@@ -8,7 +8,10 @@
 import numpy as np
 import pytest
 
-from pandas._libs.tslibs import parsing
+from pandas._libs.tslibs import (
+    parsing,
+    strptime,
+)
 from pandas._libs.tslibs.parsing import parse_time_string
 import pandas.util._test_decorators as td
 
@@ -306,7 +309,7 @@ def test_parse_time_string_check_instance_type_raise_exception():
 )
 def test_is_iso_format(fmt, expected):
     # see gh-41047
-    result = parsing.format_is_iso(fmt)
+    result = strptime.format_is_iso(fmt)
     assert result == expected