Bug report

Bug description

collections.UserString.startswith() and endswith() raise TypeError when their prefix or suffix is another UserString.

This is inconsistent with UserString.removeprefix(), removesuffix(), find(), and index(), which accept UserString arguments.

Reproducer

from collections import UserString

text = UserString("hello world")

print(text.removeprefix(UserString("hello")))
print(text.removesuffix(UserString("world")))

for method, argument in (
    ("startswith", UserString("hello")),
    ("endswith", UserString("world")),
):
    try:
        print(method, getattr(text, method)(argument))
    except TypeError as exc:
        print(method, type(exc).__name__, exc)

Actual output

 world
hello 
startswith TypeError startswith first arg must be str or a tuple of str, not UserString
endswith TypeError endswith first arg must be str or a tuple of str, not UserString

Expected behavior

Both prefix/suffix checks return True, consistently with the related UserString methods accepting UserString arguments.

Implementation details

In Lib/collections/__init__.py, UserString.startswith() and endswith() delegate directly to the underlying str without unwrapping the argument’s .data. Related methods explicitly unwrap UserString arguments.

Issue #140911 and PR #140945 fixed a similar inconsistency in UserString.index() and rindex().

This report concerns accepting UserString arguments in UserString methods, not changing str.startswith() or str.endswith() or introducing arbitrary string coercion.

CPython versions tested on:

3.14

Operating systems tested on:

macOS

Linked PRs

• gh-159868: Accept UserString arguments in startswith and endswith #159869