[Python-Dev] Usefulness of binary compatibility accross Python versions?

[Antoine Pitrou]

On Sat, 16 Dec 2017 19:37:54 +0100
Antoine Pitrou <solipsis at pitrou.net> wrote:
> 
> Currently, you can pass a `module_api_version` to PyModule_Create2(),
> but that function is for specialists only :-)
> 
> ("""Most uses of this function should be using PyModule_Create()
> instead; only use this if you are sure you need it.""")

Ah, it turns out I misunderstood that piece of documentation and also
what PEP 3121 really did w.r.t the module API check.

PyModule_Create() is actually a *macro* calling PyModule_Create2() with
the version number is was compiled against!

#ifdef Py_LIMITED_API
#define PyModule_Create(module) \
        PyModule_Create2(module, PYTHON_ABI_VERSION)
#else
#define PyModule_Create(module) \
        PyModule_Create2(module, PYTHON_API_VERSION)
#endif

And there's already a check for that version number in moduleobject.c:
https://github.com/python/cpython/blob/master/Objects/moduleobject.c#L114

That check is always invoked when calling PyModule_Create() and
PyModule_Create2().  Currently it merely invokes a warning, but we can
easily turn that into an error.

(with apologies to Martin von Löwis for not fully understanding what he
did at the time :-))

Regards

Antoine.