On Thu, Feb 24, 2022 at 11:10 PM Barry <[email protected]> wrote:
> > "Python 3.11 and newer versions use C11 without optional features. The
> > public C API should be compatible with C++."
> > https://github.com/python/peps/pull/2309/files
>
> Should is often read as meaning optional when writing specs.
> Can you say “must be compatible with C++”.
I plan to attempt to write an actual test for that, rather than a
vague sentence in a PEP. For now, "should" is a deliberate choice: I
don't know exactly which C++ version should be targeted and if it's
really an issue or not.
For example, C++20 reserves the "module" keyword, whereas Python uses
it in its C API. Example:
PyAPI_FUNC(int) PyModule_AddType(PyObject *module, PyTypeObject *type);
See:
* https://bugs.python.org/issue39355
* https://github.com/pythoncapi/pythoncapi_compat/issues/21
--
I made a change in the datatable project to add Python 3.11 support
using the pythoncapi_compat.h header file. Problem: this *C* header
file produced new warnings in datatable extension module which with
built with a C++ compiler:
https://github.com/h2oai/datatable/pull/3231#issuecomment-1032864790
Examples:
| src/core/lib/pythoncapi_compat.h:272:52: warning: zero as null
pointer constant [-Wzero-as-null-pointer-constant]
| || tstate->c_profilefunc != NULL);
| ^~~~
| nullptr
and
| src/core/lib/pythoncapi_compat.h:170:12: warning: use of old-style
cast [-Wold-style-cast]
| return (PyCodeObject *)_Py_StealRef(PyFrame_GetCode(frame));
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I made pythoncapi_compat.h compatible with C++ (fix C++ compiler
warnings) by using nullptr and reinterpret_cast<TYPE>(EXPR) cast if
the __cplusplus macro is defined, or NULL and ((TYPE)(EXPR)) cast
otherwise.
datatable also uses #include "Python.h". I don't know there were only
C++ compiler warnings on "pythoncapi_compat.h". Maybe because
datatable only uses static inline functions from
"pythoncapi_compat.h", but it may also emit the same warnings if
tomorrow some static inline functions of "Python.h" are used.
For now, I prefer to put a reminder in PEP 7 that the "Python.h" C API
is consumed by C++ projects.
Victor
--
Night gathers, and now my watch begins. It shall not end until my death.
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