`collections.UserString.rindex()` fails to accept `UserString` as `sub` argument

[T90REAL]

Bug report

Bug description:

UserString.rindex raises a TypeError when its sub argument is a UserString object. This behavior is inconsistent with UserString.rfind and most other string methods.

from collections import UserString

us = UserString("hello world")
sub = UserString("world")

assert us.rfind(sub) == us.rfind(sub.data)
assert us.rindex(sub) == us.rindex(sub.data)

Traceback (most recent call last):
  File "/src/test.py", line 7, in <module>
    assert us.rindex(sub) == us.rindex(sub.data)
           ^^^^^^^^^^^^^^
  File "/py312/lib/python3.12/collections/__init__.py", line 1553, in rindex
    return self.data.rindex(sub, start, end)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: must be str, not UserString

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• gh-140911: Ensure that UserString.rindex(), UserString.index() accept UserString as sub argument. #140945
• [3.13] gh-140911: Ensure that UserString.index() and UserString.rindex() accept UserString as argument (GH-140945) #141945
• [3.14] gh-140911: Ensure that UserString.index() and UserString.rindex() accept UserString as argument (GH-140945) #141946

[picnixz]

I can see that there is an isinstance check in rfind. It's legitimate to assume that we need one in rindex.

[serhiy-storchaka]

For reference, __contains__, count, find and replace were fixed in 98b349f. But rfind was only fixed in da2ecaf, 2.5 years later. index and rindex were missed again.