René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Callable iterator can SystemError if call exhausts the iterator","articleBody":"# Bug report\r\n\r\nIf the callable of a callable iterator (with sentinel) exhausts the iterator itself during the call, a SystemError occurs.\r\n\r\n\u003e Example discovered by @chilaxan \r\n```python\r\ndef bug():\r\n    if bug.clear:\r\n        return 1\r\n    else:\r\n        bug.clear = True\r\n        list(bug.iterator)\r\n        return 0\r\n\r\nbug.iterator = iter(bug, 1)\r\nbug.clear = False\r\nnext(bug.iterator)\r\n```\r\n```\r\nSystemError: Objects\\object.c:722: bad argument to internal function\r\n```\r\n\r\n# Likely cause\r\n`iterobject.calliter_iternext` does not check whether `it-\u003eit_sentinel` is NULL after the `_PyObject_CallNoArgs` call\r\nhttps://github.com/python/cpython/blob/main/Objects/iterobject.c#L207-L237\r\n\r\n```diff\r\nstatic PyObject *\r\ncalliter_iternext(calliterobject *it)\r\n{\r\n    PyObject *result;\r\n\r\n    if (it-\u003eit_callable == NULL) {\r\n        return NULL;\r\n    }\r\n\r\n+   result = _PyObject_CallNoArgs(it-\u003eit_callable);\r\n    if (result != NULL) {\r\n        int ok;\r\n\r\n+       ok = PyObject_RichCompareBool(it-\u003eit_sentinel, result, Py_EQ);\r\n        if (ok == 0) {\r\n            return result; /* Common case, fast path */\r\n        }\r\n(...)\r\n```\r\n\r\n# Your environment\r\nAppears to affect 3.7-3.12\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-101896\n* gh-102418\n* gh-102422\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/ionite34","@type":"Person","name":"ionite34"},"datePublished":"2023-02-13T23:27:37.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/101892/cpython/issues/101892"}