class_docstr: Base class for extension arrays implementing string methods.
  
  This is where our ExtensionArrays can override the implementation of
  Series.str.<method>. We don't expect this to work with
  3rd-party extension arrays.
  
  * User calls Series.str.<method>
  * pandas extracts the extension array from the Series
  * pandas calls ``extension_array._str_<method>(*args, **kwargs)``
  * pandas wraps the result, to return to the user.
  
  See :ref:`Series.str` for the docstring of each method.
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code: def _str_rfind(self, sub, start: int = 0, end=None):
      pass
  
imports: from __future__ import annotations
  import abc
  from typing import TYPE_CHECKING, Callable, Literal
  import numpy
label_desc: Use image node_id 13 for calling the BaseStringArrayMethods obj's underlying member method code with example usage: obj._str_rfind(sub, start, end) without return types