Builtin input does not always correctly handle errors from `PyOS_Readline`

[duaneg]

Assertion failure sending SIGINT while calling input

import os, signal, threading

send = threading.Event()

def interrupter():
 while True:
 send.wait()
 os.kill(os.getpid(), signal.SIGINT)

threading.Thread(target=interrupter).start()

send.set()
while True:
 try:
 input(">")
 except KeyboardInterrupt:
 pass

Note, this is a modified version of the example code in #112585.

Python (tested v3.12.10, v3.13.3, v3.14.0b1, and current HEAD), built with assertions enabled:

~/src/cpython/ $ ./python crash.py
>>>>>>>>>>>python: Objects/call.c:342: _PyObject_Call: Assertion `!_PyErr_Occurred(tstate)' failed.
Aborted (core dumped)

IIUC the issue is builtin_input_impl in Python/bltinmodule.c calls PyOS_Readline but assumes it cannot set an exception:

 s = PyOS_Readline(stdin, stdout, promptstr);
 if (s == NULL){
 PyErr_CheckSignals();
 if (!PyErr_Occurred())
 PyErr_SetNone(PyExc_KeyboardInterrupt);

If PyOS_Readline sets an exception (e.g. as in this case by running an interrupt signal handler itself), as opposed to being interrupted by a signal and returning NULL without setting the exception, and another signal with a handler is pending when PyErr_CheckSignals() is called, the handler will be called with the prior exception already set, and hence the assertion fails.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

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

No response

Linked PRs

• gh-134644: handle exceptions set in PyOS_Readline #134645