REF: remove unnecessary args in libparsing (#46821)

* REF: remove unnecessary args in libparsing

* mypy fixup

* mypy fixup

Author: jbrockmendel

pandas/_libs/tslibs/parsing.pyi

@@ -51,9 +51,7 @@ def try_parse_datetime_components(
 def format_is_iso(f: str) -> bool: ...
 def guess_datetime_format(
     dt_str,
-    dayfirst: bool = ...,
-    dt_str_parse=...,
-    dt_str_split=...,
+    dayfirst: bool | None = ...,
 ) -> str | None: ...
 def concat_date_cols(
     date_cols: tuple,

pandas/_libs/tslibs/parsing.pyx

@@ -872,12 +872,7 @@ def format_is_iso(f: str) -> bint:
     return False
 
 
-def guess_datetime_format(
-    dt_str,
-    bint dayfirst=False,
-    dt_str_parse=du_parse,
-    dt_str_split=_DATEUTIL_LEXER_SPLIT,
-):
+def guess_datetime_format(dt_str, bint dayfirst=False):
     """
     Guess the datetime format of a given datetime string.
 
@@ -889,20 +884,11 @@ def guess_datetime_format(
         If True parses dates with the day first, eg 20/01/2005
         Warning: dayfirst=True is not strict, but will prefer to parse
         with day first (this is a known bug).
-    dt_str_parse : function, defaults to `dateutil.parser.parse`
-        This function should take in a datetime string and return
-        a `datetime.datetime` guess that the datetime string represents
-    dt_str_split : function, defaults to `_DATEUTIL_LEXER_SPLIT` (dateutil)
-        This function should take in a datetime string and return
-        a list of strings, the guess of the various specific parts
-        e.g. '2011/12/30' -> ['2011', '/', '12', '/', '30']
 
     Returns
     -------
     ret : datetime format string (for `strftime` or `strptime`)
     """
-    if dt_str_parse is None or dt_str_split is None:
-        return None
 
     if not isinstance(dt_str, str):
         return None
@@ -934,17 +920,16 @@ def guess_datetime_format(
         datetime_attrs_to_format.insert(0, day_attribute_and_format)
 
     try:
-        parsed_datetime = dt_str_parse(dt_str, dayfirst=dayfirst)
+        parsed_datetime = du_parse(dt_str, dayfirst=dayfirst)
     except (ValueError, OverflowError):
         # In case the datetime can't be parsed, its format cannot be guessed
         return None
 
     if parsed_datetime is None:
         return None
 
-    # the default dt_str_split from dateutil will never raise here; we assume
-    #  that any user-provided function will not either.
-    tokens = dt_str_split(dt_str)
+    # _DATEUTIL_LEXER_SPLIT from dateutil will never raise here
+    tokens = _DATEUTIL_LEXER_SPLIT(dt_str)
 
     # Normalize offset part of tokens.
     # There are multiple formats for the timezone offset.

pandas/core/tools/datetimes.py

@@ -124,11 +124,11 @@ class FulldatetimeDict(YearMonthDayDict, total=False):
 # ---------------------------------------------------------------------
 
 
-def _guess_datetime_format_for_array(arr, **kwargs):
+def _guess_datetime_format_for_array(arr, dayfirst: bool | None = False):
     # Try to guess the format based on the first non-NaN element
     non_nan_elements = notna(arr).nonzero()[0]
     if len(non_nan_elements):
-        return guess_datetime_format(arr[non_nan_elements[0]], **kwargs)
+        return guess_datetime_format(arr[non_nan_elements[0]], dayfirst=dayfirst)
 
 
 def should_cache(