Move logic outside

Author: yuanx749

pandas/core/arrays/arrow/array.py

@@ -2581,7 +2581,7 @@ def _str_split(
             n = None
         if pat is None:
             split_func = pc.utf8_split_whitespace
-        elif regex or (regex is None and len(pat) != 1):
+        elif regex:
             split_func = functools.partial(pc.split_pattern_regex, pattern=pat)
         else:
             split_func = functools.partial(pc.split_pattern, pattern=pat)

pandas/core/strings/accessor.py

@@ -910,6 +910,9 @@ def split(
             )
         if is_re(pat):
             regex = True
+        elif pat is not None and regex is None:
+            # regex is None so link to old behavior #43563
+            regex = len(pat) != 1
         result = self._data.array._str_split(pat, n, expand, regex)
         if self._data.dtype == "category":
             dtype = self._data.dtype.categories.dtype

pandas/core/strings/object_array.py

@@ -339,14 +339,8 @@ def _str_split(
             new_pat: str | re.Pattern
             if regex is True or isinstance(pat, re.Pattern):
                 new_pat = re.compile(pat)
-            elif regex is False:
-                new_pat = pat
-            # regex is None so link to old behavior #43563
             else:
-                if len(pat) == 1:
-                    new_pat = pat
-                else:
-                    new_pat = re.compile(pat)
+                new_pat = pat
 
             if isinstance(new_pat, re.Pattern):
                 if n is None or n == -1: