[Python-Dev] Experiment an opt-in new C API for Python? (leave current API unchanged)

[Neil Schemenauer]

On 2018-11-16, Nathaniel Smith wrote:
> [..] it seems like you should investigate (a) whether you can make
> Py_LIMITED_API *be* that API, instead of having two different
> ifdefs

That might be a good idea.  One problem is that we might like to
make backwards incompatible changes to Py_LIMITED_API.  Maybe it
doesn't matter if no extensions actually use Py_LIMITED_API.
Keeping API and ABI compatibility with the existing Py_LIMITED_API
could be difficult.

What would be the downside of using a new CPP define?  We could
deprecate Py_LIMITED_API and the new API could do the job.

Also, I think extensions should have to option to turn the ABI
compatibility off.  For some extensions, they will not want to
convert if there is a big performance hit (some macros turn into
non-inlined functions, call functions rather than access a
non-opaque structure).

Maybe there is a reason my toggling idea won't work.  If we can use
a CPP define to toggle between inline and non-inline functions, I
think it should work.  Maybe it will get complicated.

Providing ABI compatibility like Py_LIMITED_API is a different goal
than making the API more friendly to alternative Python VMs.  So,
maybe it is a mistake to try to tackle both goals at once.  However,
the goals seem closely related and so it would be a shame to do a
bunch of work and not achieve both.


Regards,

  Neil