Bug report

If the callable of a callable iterator (with sentinel) exhausts the iterator itself during the call, a SystemError occurs.

Example discovered by @chilaxan

def bug(): if bug.clear: return 1 else: bug.clear = True list(bug.iterator) return 0 bug.iterator = iter(bug, 1) bug.clear = False next(bug.iterator)

SystemError: Objects\object.c:722: bad argument to internal function 

Likely cause

iterobject.calliter_iternext does not check whether it->it_sentinel is NULL after the _PyObject_CallNoArgs call
https://github.com/python/cpython/blob/main/Objects/iterobject.c#L207-L237

static PyObject * calliter_iternext(calliterobject *it) { PyObject *result; if (it->it_callable == NULL) { return NULL; } + result = _PyObject_CallNoArgs(it->it_callable); if (result != NULL) { int ok; + ok = PyObject_RichCompareBool(it->it_sentinel, result, Py_EQ); if (ok == 0) { return result; /* Common case, fast path */ } (...)

Your environment

Appears to affect 3.7-3.12

Linked PRs

• gh-101892: Fix SystemError when a callable iterator call exhausts the iterator #101896
• [3.11] gh-101892: Fix SystemError when a callable iterator call exhausts the iterator (GH-101896) #102418
• [3.10] gh-101892: Fix SystemError when a callable iterator call exhausts the iterator (GH-101896) #102422