keep format_is_iso as cdef, make def wrapper for test

Author: MarcoGorelli

pandas/_libs/tslibs/strptime.pxd

@@ -1,5 +1,4 @@
 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

@@ -54,7 +54,7 @@ from pandas._libs.tslibs.timestamps import Timestamp
 
 cnp.import_array()
 
-cpdef bint format_is_iso(f: str):
+cdef 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
@@ -74,6 +74,11 @@ cpdef bint format_is_iso(f: str):
     return False
 
 
+def _test_format_is_iso(f: str) -> bool:
+    """Only used in testing."""
+    return format_is_iso(f)
+
+
 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

pandas/tests/tslibs/test_parsing.py

@@ -315,7 +315,7 @@ def test_parse_time_string_check_instance_type_raise_exception():
 )
 def test_is_iso_format(fmt, expected):
     # see gh-41047
-    result = strptime.format_is_iso(fmt)
+    result = strptime._test_format_is_iso(fmt)
     assert result == expected