REF: remove unnecessary string mixin

Author: jbrockmendel

pandas/core/strings/__init__.py

@@ -2,25 +2,21 @@
 Implementation of pandas.Series.str and its interface.
 
 * strings.accessor.StringMethods : Accessor for Series.str
-* strings.base.BaseStringArrayMethods: Mixin ABC for EAs to implement str methods
 
 Most methods on the StringMethods accessor follow the pattern:
 
     1. extract the array from the series (or index)
     2. Call that array's implementation of the string method
     3. Wrap the result (in a Series, index, or DataFrame)
 
-Pandas extension arrays implementing string methods should inherit from
-pandas.core.strings.base.BaseStringArrayMethods. This is an ABC defining
-the various string methods. To avoid namespace clashes and pollution,
+To avoid namespace clashes and pollution,
 these are prefixed with `_str_`. So ``Series.str.upper()`` calls
 ``Series.array._str_upper()``. The interface isn't currently public
 to other string extension arrays.
 """
 # Pandas current implementation is in ObjectStringArrayMixin. This is designed
 # to work on object-dtype ndarrays.
 #
-# BaseStringArrayMethods
 #  - ObjectStringArrayMixin
 #     - StringArray
 #     - NumpyExtensionArray

pandas/core/strings/base.py

@@ -21,8 +21,6 @@
 from pandas.core.dtypes.common import pandas_dtype
 from pandas.core.dtypes.missing import isna
 
-from pandas.core.strings.base import BaseStringArrayMethods
-
 if TYPE_CHECKING:
     from collections.abc import (
         Callable,
@@ -35,7 +33,7 @@
     )
 
 
-class ObjectStringArrayMixin(BaseStringArrayMethods):
+class ObjectStringArrayMixin:
     """
     String Methods operating on object-dtype ndarrays.
     """
@@ -44,6 +42,12 @@ def __len__(self) -> int:
         # For typing, _str_map relies on the object being sized.
         raise NotImplementedError
 
+    def _str_getitem(self, key):
+        if isinstance(key, slice):
+            return self._str_slice(start=key.start, stop=key.stop, step=key.step)
+        else:
+            return self._str_get(key)
+
     def _str_map(
         self,
         f,