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[C API] Promote PEP 523 functions to public functions: add PyUnstable_InterpreterState_SetEvalFrameFunc() #141518
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A code search on PyPI top 15,000 projects using regex
_PyInterpreterState_GetEvalFrameFunc|_PyInterpreterState_SetEvalFrameFunc|_PyEval_EvalFrameDefaultdidn't find_PyInterpreterState_GetEvalFrameFunc()or_PyInterpreterState_SetEvalFrameFunc()usage, but found_PyEval_EvalFrameDefault()usage in 7 projects:- cython (3.1.4)
- debugpy (1.8.17)
- memray (1.18.0)
- numpy (2.3.3)
- ptvsd (4.3.2)
- pystack (1.5.1)
- river (0.22.0)
Details
cython-3.1.4.tar.gz: cython-3.1.4/Cython/Debugger/libpython.py: EVALFRAME = '_PyEval_EvalFrameDefault' debugpy-1.8.17.tar.gz: debugpy-1.8.17/src/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: #define CALL_EvalFrameDefault_39(a, b, c) _PyEval_EvalFrameDefault(a, b, c) debugpy-1.8.17.tar.gz: debugpy-1.8.17/src/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: #define CALL_EvalFrameDefault_38(a, b) _PyEval_EvalFrameDefault(a, b) debugpy-1.8.17.tar.gz: debugpy-1.8.17/src/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: PyObject* _PyEval_EvalFrameDefault(...) debugpy-1.8.17.tar.gz: debugpy-1.8.17/src/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: state.interp.eval_frame = _PyEval_EvalFrameDefault debugpy-1.8.17.tar.gz: debugpy-1.8.17/src/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.template.pyx: state.interp.eval_frame = _PyEval_EvalFrameDefault memray-1.18.0.tar.gz: memray-1.18.0/src/memray/_memray.pyx: if pidx >= 0 and "_PyEval_EvalFrameDefault" in symbol: memray-1.18.0.tar.gz: memray-1.18.0/src/memray/_memray.pyx: if function != "_PyEval_EvalFrameDefault": memray-1.18.0.tar.gz: memray-1.18.0/src/memray/reporters/frame_tools.py: if "PyEval_EvalFrameEx" in symbol or "_PyEval_EvalFrameDefault" in symbol: numpy-2.3.3.tar.gz: numpy-2.3.3/numpy/_core/src/multiarray/temp_elide.c: #define PYFRAMEEVAL_FUNC "_PyEval_EvalFrameDefault" ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: PyObject* _PyEval_EvalFrameDefault(PyFrameObject *frame, int exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: return _PyEval_EvalFrameDefault(frame_obj, exc) ptvsd-4.3.2.zip: ptvsd-4.3.2/src/ptvsd/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pyx: state.interp.eval_frame = _PyEval_EvalFrameDefault pystack-1.5.1.tar.gz: pystack-1.5.1/src/pystack/types.py: return "_PyEval_EvalFrameDefault" in symbol river-0.22.0.tar.gz: river-0.22.0/.venv/lib/python3.13/site-packages/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: #define CALL_EvalFrameDefault_39(a, b, c) _PyEval_EvalFrameDefault(a, b, c) river-0.22.0.tar.gz: river-0.22.0/.venv/lib/python3.13/site-packages/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: #define CALL_EvalFrameDefault_38(a, b) _PyEval_EvalFrameDefault(a, b) river-0.22.0.tar.gz: river-0.22.0/.venv/lib/python3.13/site-packages/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.pxd: PyObject* _PyEval_EvalFrameDefault(...) river-0.22.0.tar.gz: river-0.22.0/.venv/lib/python3.13/site-packages/debugpy/_vendored/pydevd/_pydevd_frame_eval/pydevd_frame_evaluator.template.pyx: state.interp.eval_frame = _PyEval_EvalFrameDefaultPyCharm blog post from 2017 about PEP 523 APIs: https://blog.jetbrains.com/pycharm/2017/03/inside-the-debugger-interview-with-elizaveta-shashkova/
What changed in Python 3.6 to allow this?
The new frame evaluation API was introduced to CPython in PEP 523 and it allows to specify a per-interpreter function pointer to handle the evaluation of frames.PyTorch Dynamo says that it uses the PEP 523 API: https://docs.pytorch.org/docs/stable/torch.compiler_dynamo_overview.html
Dynamo hooks into the frame evaluation API in CPython (PEP 523) to dynamically modify Python bytecode right before it is executed.
Perhaps it would be better to make these
PyUnstablefunctions? I believe there was discussion at PyCon this year (and it seems in the past) about issues with the frame evaluation C API. Looping in a few people who probably have stronger opinions than I:
@markshannon
@jansel
@itamaroReacted by Petr ViktorinPyTorch's torch.compile uses PEP 523. PyUnstable would be fine for us. We already need to do extra work to support each new Python version primarily due to Python bytecode changes.
A code search on PyPI top 15,000 projects using regex...
Those are either:
- a vendored old version of pydevd. All debuggers now use
sys.monitoring - pystack/memray -- They both probe into CPython internals, so don't much care about APIs.
The only use case that matters, and probably the only use case at all, is PyTorch.
I don't want to make the API public because that entails a lot of defining semantics and guarantees about future compatibility. It also effectively makes the interpreter frame part of the public API, and I don't want that either.
Making them
PyUnstableseems best.Reacted by Emma Smith and Mikhail Efimov- a vendored old version of pydevd. All debuggers now use
- changed the title
[-][C API] Promote PEP 523 functions to public functions: add `PyInterpreterState_SetEvalFrameFunc()`[/-][+][C API] Promote PEP 523 functions to public functions: add `PyUnstable_InterpreterState_SetEvalFrameFunc()`[/+]on Nov 14, 2025 As long as the frame evaluation API provides the functionality along PEP 523 spirit, I don't think it matters to us (cinder jit in this context) what's the exact spelling. Right @DinoV ?
Correct, a rename is no big deal, I think this probably just predated the PyUnstable convention.
Reacted by Emma Smith, Mikhail Efimov and Victor StinnerThe C API Working Group decided to not add a public function for this feature, but keep the
_Pyname instead: capi-workgroup/decisions#89.
C extensions should not use private functions (functions prefixed by
_Py), but PEP 523 only added private functions:_PyInterpreterState_GetEvalFrameFunc()_PyInterpreterState_SetEvalFrameFunc()_PyEval_EvalFrameDefault()I propose promoting these functions as public functions (just remove the
_prefix):PyUnstable_InterpreterState_GetEvalFrameFunc()PyUnstable_InterpreterState_SetEvalFrameFunc()PyUnstable_Eval_EvalFrameDefault()cc @emmatyping
Update: I added
PyUnstable_prefix to function names.Linked PRs