Segfault in Interpreter.exec() when the uncaught exception's __str__ raises #161996

Crash report

A custom exception whose __str__ also raises will crash the process when it is raised in a subinterpreter.

from concurrent import interpreters

interp = interpreters.create()
interp.exec("""
class MyError(Exception):
    def __str__(self):
        raise ValueError

raise MyError
""")

Assertion failed: (_PyErr_Occurred(tstate)), function _PyXI_Exit, file crossinterp.c, line 2872.
fish: Job 1, './python.exe a.py' terminated by signal SIGABRT (Abort)

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

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

No response

Linked PRs

• gh-161996: Fix crash in Interpreter.exec() when the uncaught exception's __str__ raises #162000