describe PyEval_CallObjectWithKeywords and its replacement

[jwuttke]

BPO	42181
Nosy	@jdemeyer, @jwuttke

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-10-28.14:18:31.385>
labels = ['expert-C-API', '3.9']
title = 'describe PyEval_CallObjectWithKeywords and its replacement'
updated_at = <Date 2020-10-28.14:18:31.385>
user = 'https://github.com/jwuttke'

bugs.python.org fields:

activity = <Date 2020-10-28.14:18:31.385>
actor = 'jwuttke'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2020-10-28.14:18:31.385>
creator = 'jwuttke'
dependencies = []
files = []
hgrepos = []
issue_num = 42181
keywords = []
message_count = 1.0
messages = ['379828']
nosy_count = 2.0
nosy_names = ['jdemeyer', 'jwuttke']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue42181'
versions = ['Python 3.9']

[jwuttke]

The current 3.9 docs do not describe PyEval_CallObjectWithKeywords, among other PyEval_CallObject* functions.

Yes, I know, these functions are deprecated. But they are still part of the API; they ought to be documented.

Rather, given that they are deprecated, there is more need than ever to document them: The documentation should specify when they have been deprecated, until then they are guaranteed to be supported, and most importantly, how they are to be replaced.

Fulltext search leads me to the 3.9 Changelog that says: »PyEval_CallFunction, PyEval_CallMethod and PyEval_CallObjectWithKeywords are deprecated. Use PyObject_Call() and its variants instead.« This is far not enough. As a maintainer of 3rd-party code with no knowledge of and no interest in the Python C API, I do not want to spend half a day on finding out which variant to use, and how argument lists differ.

[Mekk]

+1. Just searching how should I replace that…

[Mekk]

In the end I had to replace

PyObject* ret = PyEval_CallObjectWithKeywords(func, arg, kw);

with

if (arg != NULL && ! PyTuple_Check(arg)) {
    PyErr_SetString(PyExc_TypeError,
                    "argument list must be a tuple");
    return NULL;
}
if (kw != NULL && !PyDict_Check(kw)) {
    PyErr_SetString(PyExc_TypeError,
                    "keyword list must be a dictionary");
    return NULL;
}
PyObject* ret = (arg == NULL)
    ? _PyObject_FastCallDict(func, NULL, 0, kw)
    : PyObject_Call(func, arg, kw);

so I think that the decision to deprecate the former was made without appropriate consideration (replacement is much longer and I had to use private function).

[sparkprime]

I'm seeing this deprecation warning now and I'm not sure what to do about it.