Bug report

Bug description:

There are 3 callers of _PyFrame_GetFrameObject which explicitly clear error when it returns NULL.

1. take_ownership

   cpython/Python/frame.c

   Lines 74 to 79 in b67a64d

   	PyFrameObject *back = _PyFrame_GetFrameObject(prev);
   	if (back == NULL) {
   	/* Memory error here. */
   	assert(PyErr_ExceptionMatches(PyExc_MemoryError));
   	/* Nothing we can do about it */
   	PyErr_Clear();

2. PyEval_GetFrame

   cpython/Python/ceval.c

   Lines 2562 to 2564 in b67a64d

   	PyFrameObject *f = _PyFrame_GetFrameObject(frame);
   	if (f == NULL) {
   	PyErr_Clear();

3. PyThreadState_GetFrame

   cpython/Python/pystate.c

   Lines 2101 to 2103 in b67a64d

   	PyFrameObject *frame = _PyFrame_GetFrameObject(f);
   	if (frame == NULL) {
   	PyErr_Clear();

PyEval_GetFrame and PyThreadState_GetFrame docs say that NULL is returned when "no frame is currently executing", and doesn't say anything about any error (probably as they explicitly clear it?).

I wonder whether PyFrame_GetBack also would want to clear error

PyFrame_GetBack's documentation doesn't say anything about MemoryError which can be set by its internal API calls https://docs.python.org/3.15/c-api/frame.html#c.PyFrame_GetBack

The rest of the _PyFrame_GetFrameObject callers that don't clear error including PyFrame_GetBack are

• _PyEval_ExceptionGroupMatch
• _PyEval_EvalFrameDefault (error label)
• _gen_getframe
• sys__getframe_impl
• _PyThread_CurrentFrames
• _Py_call_instrumentation_line
• _PyFrame_GetLocals
• PyEval_GetLocals — Public C API (deprecated), no NULL check
• PyFrame_GetBack — Public C API, no NULL check

And PyEval_GetLocals and PyFrame_GetBack are public C APIs that don't check for NULL and don't clear the error. I guess the internals are ok to propagate the errors?

Can someone explain whether PyFrame_GetBack not clearing error on null is ok/intended or it's a discrepancy/bug?

I would prefer PyFrame_GetBack to not propagate an error given that its documentation doesn't say anything about MemoryError.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-144693: Clarify that PyFrame_GetBack does not raises exception #144824
• [3.14] gh-144693: Clarify that PyFrame_GetBack does not raise exceptions (GH-144824) #145318
• [3.13] gh-144693: Clarify that PyFrame_GetBack does not raise exceptions (GH-144824) #145319