New submission from STINNER Victor <vstin...@python.org>:
There are more and more popular projects using the Python C API. The first big player is pybind11: "Seamless operability between C++11 and Python" https://pybind11.readthedocs.io/ Recently, I proposed a PR to add Python 3.11 support to the datatable project: https://github.com/h2oai/datatable/pull/3231 My PR uses pythoncapi_compat.h header file which provides recent C API functions to old Python functions. The header file implements these functions as static inline function. Problem: a static inline function implemented in a C header file used in a C++ code file can emit C++ compiler warnings. In datatable, I got two kinds of C++ compiler warnings: * Usage of the C NULL constant: C++ prefers nullptr * "Old-style" cast like (PyObject*)obj: C++ prefers static_cast, reinterpret_cast, etc. It seems like these compiler warnings are not enabled by default. The datatable project seems enabling them in its CI and I was asked to fix these warnings. In the pythoncapi-compat project (*), I chose to use nullptr and reinterpret_cast if the "__cplusplus" macro is defined. Example: --- // C++ compatibility #ifdef __cplusplus # define PYCAPI_COMPAT_CAST(TYPE, EXPR) reinterpret_cast<TYPE>(EXPR) # define PYCAPI_COMPAT_NULL nullptr #else # define PYCAPI_COMPAT_CAST(TYPE, EXPR) ((TYPE)(EXPR)) # define PYCAPI_COMPAT_NULL NULL #endif // Cast argument to PyObject* type. #ifndef _PyObject_CAST # define _PyObject_CAST(op) PYCAPI_COMPAT_CAST(PyObject*, op) #endif --- (*) https://github.com/python/pythoncapi_compat It's unclear to me if the Python C API has or has not the same issue than pythoncapi_compat.h. Last years, some old macros of the Python C API have been converted to static inline functions, like Py_INCREF(). It's unclear to me if these compiler warnings happen on Py_INCREF(). I don't understand why, but static inline macros from Python.h didn't emit compiler warnings in datatable, whereas similar static inline functions of pythoncapi_compat.h emitted compiler warnings. Maybe there is a difference between <Python.h> and "Python.h". Or maybe it depends if the header file is a "local" file, or a "system" header file (ex: installed in /usr/include/ on Linux). A first step would be to build a C++ extension as part of the Python test suite and check that there is no compiler warning. My GH-32175 PR is a proof-of-concept of that. I don't know which C++ version we should target. pybind11 targets C++11. See bpo-39355 for a discussion about C++20: usage of the C++20 "module" keyword... which is a "contextual keyword" in practice. ---------- components: C API messages: 416359 nosy: vstinner priority: normal severity: normal status: open title: [C API] Test that the Python C API is compatible with C++ type: enhancement versions: Python 3.11 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue47165> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com