use enum

Author: MarcoGorelli

pandas/_libs/tslib.pyx

@@ -28,6 +28,7 @@ cnp.import_array()
 
 from pandas._libs.tslibs.np_datetime cimport (
     NPY_DATETIMEUNIT,
+    Exact,
     NPY_FR_ns,
     check_dts_bounds,
     get_datetime64_value,
@@ -411,7 +412,7 @@ cpdef array_to_datetime(
     bint utc=False,
     bint require_iso8601=False,
     format: str | None=None,
-    bint exact=True,
+    Exact exact=Exact.EXACT_MATCH,
 ):
     """
     Converts a 1D array of date-like values to a numpy array of either:

pandas/_libs/tslibs/np_datetime.pxd

@@ -9,6 +9,11 @@ from numpy cimport (
 )
 
 
+cdef enum Exact:
+    INEXACT_MATH
+    EXACT_MATCH
+    NO_MATCH
+
 # TODO(cython3): most of these can be cimported directly from numpy
 cdef extern from "numpy/ndarrayobject.h":
     ctypedef int64_t npy_timedelta
@@ -96,7 +101,7 @@ cdef int string_to_dts(
     int* out_tzoffset,
     bint want_exc,
     format: str | None = *,
-    int exact = *
+    Exact exact = *
 ) except? -1
 
 cdef NPY_DATETIMEUNIT get_unit_from_dtype(cnp.dtype dtype)

pandas/_libs/tslibs/np_datetime.pyx

@@ -279,7 +279,7 @@ cdef int string_to_dts(
     int* out_tzoffset,
     bint want_exc,
     format: str | None=None,
-    int exact=1,
+    Exact exact=EXACT_MATCH,
 ) except? -1:
     cdef:
         Py_ssize_t length
@@ -291,7 +291,7 @@ cdef int string_to_dts(
     if format is None:
         format_buf = b""
         format_length = 0
-        exact = 2
+        exact = NO_MATCH
     else:
         format_buf = get_c_string_buf_and_size(format, &format_length)
     return parse_iso_8601_datetime(buf, length, want_exc,