Crash report

What happened?

It's possible to make the interpreter abort by calling_interpreters.run_string with an instance of a subclass ofstr as thescript argument:

import_interpretersclassweird_str(str):pass_interpreters.create()_interpreters.run_string(1,weird_str('1'))python: ./Modules/_interpretersmodule.c:333:get_code_str:Assertion `PyUnicode_CheckExact(arg)&& (check_code_str((PyUnicodeObject*)arg)==NULL)'failed.Aborted (coredumped)

This happens because, after a check thatarg is astr or subclass, there's an assertion thatarg is exactly an instance ofstr:

if (PyUnicode_Check(arg)) {assert(PyUnicode_CheckExact(arg)&& (check_code_str((PyUnicodeObject*)arg)==NULL));

Found usingfusil by@vstinner.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.14.0a6+ (heads/main:04bc681e7cf, Apr 4 2025, 12:38:19) [GCC 11.4.0]

Linked PRs

• gh-132171: Fix_interpreters.run_string crash on string subclass #132173
• [3.13] gh-132171: Fix_interpreters.run_string crash on string subclass (GH-132173) #132219