bpo-30459: Cast the result of PyList_SET_ITEM() to void

[ZackerySpytz]

Do the same for PyTuple_SET_ITEM().

https://bugs.python.org/issue30459

[vstinner]

If a change is made, I would prefer to convert this macro to a static inline function. You need to keep a macro for _PyList_CAST(). For example, declare the static inline function with name _PyList_SET_ITEM(). See Py_INCREF() for another example. Also, while we are here, I would prefer to use better name than "i" and "v". For example: PyList_SET_ITEM(list, index, value).

[vstinner]

The initial issue seems to show that PyList_SET_ITEM() result can be used, but also that it is used in practice:
https://bugs.python.org/issue30459#msg294362

So I would suggest to document in the C API changes, Porting to Python 3.9:
https://docs.python.org/dev/whatsnew/3.9.html#id2

[vstinner]

By the way, I added Py_SET_REFCNT(), Py_SET_TYPE() and Py_SET_SIZE() in Python 3.9, but I left the related Py_REFCNT(), Py_TYPE() and Py_SIZE() unchanged. It remains possible to use them as l-value for example: Py_REFCNT(ob) = 1;.

I expect that few C extensions use Py_REFCNT(ob) = 1;, but maybe a few use Py_TYPE(op) = type;. For Py_SIZE(ob) = size;, Python 3.8 didn't provide any "abstract" setter function/macro, direct access to the member is also possible: ((PyVarObject*)ob)->ob_size = size;,

I chose to add new macros in Python 3.9, and maybe change the macros in Python 3.10. The change is part of a larger project:
https://github.com/vstinner/misc/blob/master/cpython/pep-opaque-c-api.rst

See bpo-39573.

[vstinner]

No activity since May, I close the PR. I created PR #23645 which converts PyTuple_SET_ITEM() and PyList_SET_ITEM() to static inline functions.

[vstinner]

Thanks @ZackerySpytz, I merged your PR. I wrote PR #23654 to modify also PyCell_SET().