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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Builtin input does not always correctly handle errors from `PyOS_Readline`","articleBody":"### Assertion failure sending `SIGINT` while calling `input`\n```python\nimport os, signal, threading\n\nsend = threading.Event()\n\ndef interrupter():\n    while True:\n        send.wait()\n        os.kill(os.getpid(), signal.SIGINT)\n\nthreading.Thread(target=interrupter).start()\n\nsend.set()\nwhile True:\n    try:\n        input(\"\u003e\")\n    except KeyboardInterrupt:\n        pass\n```\n\nNote, this is a modified version of the example code in #112585.\n\nPython (tested `v3.12.10`,  `v3.13.3`, `v3.14.0b1`, and current `HEAD`), built with assertions enabled:\n```\n~/src/cpython/ $ ./python crash.py\n\u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003epython: Objects/call.c:342: _PyObject_Call: Assertion `!_PyErr_Occurred(tstate)' failed.\nAborted (core dumped)\n```\n\nIIUC the issue is `builtin_input_impl` in `Python/bltinmodule.c` calls `PyOS_Readline` but assumes it cannot set an exception:\n```\n    s = PyOS_Readline(stdin, stdout, promptstr);\n    if (s == NULL) {\n        PyErr_CheckSignals();\n        if (!PyErr_Occurred())\n            PyErr_SetNone(PyExc_KeyboardInterrupt);\n```\n\nIf `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.\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n### Output from running 'python -VV' on the command line:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-134645\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/duaneg","@type":"Person","name":"duaneg"},"datePublished":"2025-05-25T04:31:22.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/134644/cpython/issues/134644"}