On 27/09/2021 16.32, Ronald Oussoren via Python-Dev wrote:
On 26 Sep 2021, at 19:03, Christian Heimes <christ...@python.org
<mailto:christ...@python.org>> wrote:
On 26/09/2021 13.07, jack.jan...@cwi.nl <mailto:jack.jan...@cwi.nl> wrote:
The problem with the stable ABI is that very few developers are
targeting it. I’m not sure why not, whether it has to do with
incompleteness of the ABI, or with issues targeting it easily and
your builds and then having pip/PyPI do the right things with wheels
and all that. I’ve been on the capi-sig mailing list since its
inception in 2007, but the discussions are really going over my head.
I don’t understand what the problems are that keep people from
targeting the stable ABI (or the various other attempts at
standardising extensions over Python versions).
It takes some effort to port old extensions to stable ABI. Several old
APIs are not supported in stable ABI extensions. For example
developers have to port static type definitions to heap types. It's
not complicated, but it takes some effort.
The stable ABI is also not complete, although it should be complete
enough for a lot of projects. A, fairly esoteric, issue I ran into is
that it is currently not possible to define a class with a non-default
meta class using the type-spec API (AFAIK), see #15870.
And as you write “it takes some effort”, that alone likely reduces the
amount of projects that migrate to the stable ABI esp. for projects that
already have a CI/CD setup that creates binary wheels for you (for
example using cibuildwheel).
Indeed, the stable ABI is not complete. I just figured out that limited
API < 3.9 cannot define objects with weakref support or dict offset. The
__weaklistoffset__ and __dictoffset__ PyMemberDefs were added in Python
3.9.
Christian
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