PyMemberDef missing in limited API / Deprecate structmember.h

[benjaminp]

BPO	2897
Nosy	@loewis, @smontanaro, @birkenfeld, @rhettinger, @abalkin, @vstinner, @benjaminp, @berkerpeksag, @serhiy-storchaka, @matrixise, @erlend-aasland, @MatzeB
PRs	bpo-2897: Make PyMemberDef part of stable ABI; deprecate structmember.h #20462 bpo-41861: Clean up sqlite3 header files wrt. PEP 384 #22419
Dependencies	bpo-24065: Outdated *_RESTRICTED flags in structmember.h bpo-28349: Issues with PyMemberDef flags
Files	issue2897.diff issue2897-docs-3x.diff

^{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 = 'https://github.com/abalkin'
closed_at = None
created_at = <Date 2008-05-16.22:45:11.685>
labels = ['interpreter-core', 'expert-C-API', 'type-feature', '3.10', 'docs']
title = 'PyMemberDef missing in limited API / Deprecate structmember.h'
updated_at = <Date 2020-09-26.20:51:31.703>
user = 'https://github.com/benjaminp'

bugs.python.org fields:

activity = <Date 2020-09-26.20:51:31.703>
actor = 'erlendaasland'
assignee = 'belopolsky'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Interpreter Core', 'C API']
creation = <Date 2008-05-16.22:45:11.685>
creator = 'benjamin.peterson'
dependencies = ['24065', '28349']
files = ['44943', '44976']
hgrepos = []
issue_num = 2897
keywords = ['patch']
message_count = 21.0
messages = ['66972', '67028', '67062', '79242', '79244', '277971', '277973', '277976', '277982', '277985', '277986', '277988', '278136', '342468', '370098', '370100', '370101', '370104', '370106', '370107', '370138']
nosy_count = 15.0
nosy_names = ['loewis', 'skip.montanaro', 'georg.brandl', 'rhettinger', 'belopolsky', 'vstinner', 'benjamin.peterson', 'Arfrever', 'herzbube', 'docs@python', 'berker.peksag', 'serhiy.storchaka', 'matrixise', 'erlendaasland', 'Matthias Braun']
pr_nums = ['20462', '22419']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue2897'
versions = ['Python 3.10']

• PR: gh-47146: Soft-deprecate structmember.h, expose its contents via Python.h #99014

• PR: gh-47146: Fix reference counting in _testcapi.structmember initializer #106862

• PR: [3.12] gh-47146: Fix reference counting in _testcapi.structmember initializer (GH-106862) #106953

[benjaminp]

As the comment in descrobject.c says:

/* Why is this not included in Python.h? */

[birkenfeld]

We could include it in Py3k.

[abalkin]

Note that structmember.h pollutes global namespace with macros that do not
have conventional Py_ or PY_ prefix. READONLY and RESTRICTED macros seem
to be most likely to conflict with other code. I would be -0 on including tructmember.h in Python.h if flags macros are not properly renamed. +0
otherwise. T_* macros are probably OK, but T prefix is reminiscent of
popular (in some circles) Taligent naming conventions:

http://pcroot.cern.ch/TaligentDocs/TaligentOnline/DocumentRoot/1.0/Docs/bo
oks/WM/WM_63.html#HEADING77

[rhettinger]

Martin, do you want to make the call on this one?

[loewis]

I agree with Alexander; the header shouldn't be included into Python.h
as-is.

I would propose to eliminate it eventually, with the following steps:

1. move PyMemberDef and the function declarations into object.h
2. (simultaneously) introduce properly-prefixed macros in object.h
3. deprecate structmember.h
4. remove it

[abalkin]

I am attaching a patch that implements steps 1 and 2 of Martin's plan. There are over 50 files that include structmember.h. I am not sure it is worth the trouble to update all those files before structmember.h is actually removed. If we agree that this is the right way forward, I'll make the necessary changes to the docs.

[abalkin]

I would also like this opportunity to rename T_PYSSIZET to something more readable: maybe PY_T_PY_SSIZE_T or PY_T_SSIZE_T.

[serhiy-storchaka]

Please don't forget to use "hg copy" for creating object.h from structmember.h. This preserves the history.

structmember.h should be implemented using object.h. Include object.h and add aliases.

Only READONLY flag is used in 3.x (bpo-28349). Other flags can be removed.