[Python-Dev] C API changes

[Steve Dower]

On 30Nov2018 1133, Antoine Pitrou wrote:
> On Fri, 30 Nov 2018 13:06:11 -0600
> Neil Schemenauer <nas-python at arctrix.com> wrote:
>> On 2018-11-29, Armin Rigo wrote:
>>> ...Also, although I'm discussing it here, I think the whole approach
>>> would be better if done as a third-party extension for now, without
>>> requiring changes to CPython---just use the existing C API to
>>> implement the CPython version.
>>
>> Hello Armin,
>>
>> Thank you for providing your input on this subject.  I too like the
>> idea of an API "shim layer" as a separate project.
>>
>> What do you think of writing the shim layer in C++?  I'm not a C++
>> programmer but my understanding is that modern C++ compilers are
>> much better than years ago.  Using C++ would allow us to provide a
>> higher level API with smaller runtime costs.
> 
> The main problem with exposing a C++ *API* is that all people
> implementing that API suddenly must understand and implement the C++
> *ABI* (with itself varies from platform to platform :-)).  That's
> trivially easy if your implementation is itself written in C++, but not
> if it's written in something else such as RPython, Java, Rust, etc.
> 
> C is really the lingua franca when exposing an interface that can be
> understood, implemented and/or interfaced with from many different
> languages.
> 
> So I'd turn the proposal on its head: you can implement the internals
> of your interpreter or object layer in C++ (and indeed I think it
> would be crazy to start writing a new Python VM in raw C), but you
> should still expose a C-compatible API for third-party providers and
> consumers.

I totally agree with Antoine here. C++ is great for internals, but not 
the public interfaces.

The one additional point I'd add is that there are other ABIs that C++ 
can use (such as xlang, Corba and COM), which can provide stability in 
ways the plain-old C++ ABI does not. So we wouldn't necessarily have to 
design a new C-based ABI for this, we could adopt an existing one that 
is already proven and already has supporting tools.

Cheers,
Steve