[Python-Dev] Re: Expected stability of PyCode_New() and types.CodeType() signatures

Victor Stinner wrote:

Update.

Le ven. 31 mai 2019 à 10:49, Petr Viktorin

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PEP 570 (Positional-Only Parameters) changed the signatures of PyCode_New() and types.CodeType(), adding a new argument for "posargcount".

Pablo proposed a PR to revert PyCode_New() API to Python 3.7 API: https://github.com/python/cpython/pull/13959

I dislike "PyCode_NewEx" name, it will become worse when another parameter will be added in the future. I prefer "With" naming. I prefer "PyCode_NewWithPosArgs()" name.

I agree if a new name is chosen (I haven't decided if the parameter expansion was wrong or not in practice or if this was just poorly communicated). -Brett

For types.CodeType constructor, well, I added CodeType.replace() to help projects to be prepared for next CodeType constructor change :-) But *I* am fine with breaking this constructor since very few projects create explicitly code objects.

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Our policy for such changes seems to be fragmented tribal knowledge. I'm writing to check if my understanding is reasonable, so I can apply it and document it explicitly. The doc has been updated: https://bugs.python.org/issue36896

"If you instantiate any of these types, note that signatures may vary between Python versions."

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There is a surprisingly large ecosystem of tools that create code objects. The expectation seems to be that these tools will need to be adapted for each minor version of Python. For PyCode_New() change, it seems like (almost?) only projects using Cython are affected, no?

To not require Cython when they are installed, many projects include C files generated by Cython in their tarball (and other released files).

So yeah, the PyCode_New() change is very annoying in practical, since every single project using Cython requires a new release in practice.

For this reason, I'm in favor of reverting PyCode_New() API and add a new function with the extra positional only parameter.

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Also, the expected level of API stability should be documented in the docs. Note: code.h header is excluded from the stable API :-) The whole file is surrounded by "#ifndef Py_LIMITED_API".

Victor -- Night gathers, and now my watch begins. It shall not end until my death.