Py_tp_dictoffset / Py_tp_finalize are unsettable in stable API

[DinoV]

BPO	38140
Nosy	@DinoV, @encukou, @ericsnowcurrently, @eduardo-elizondo, @shihai1991
PRs	bpo-38140: Make dict and weakref offsets opaque for C heap types #16076 bpo-38140: Document offsets in PyMemberDef #16354

^{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/DinoV'
closed_at = <Date 2019-10-08.12:18:12.316>
created_at = <Date 2019-09-12.14:04:20.667>
labels = ['interpreter-core', '3.9']
title = 'Py_tp_dictoffset / Py_tp_finalize are unsettable in stable API'
updated_at = <Date 2019-10-08.12:18:12.314>
user = 'https://github.com/DinoV'

bugs.python.org fields:

activity = <Date 2019-10-08.12:18:12.314>
actor = 'petr.viktorin'
assignee = 'dino.viehland'
closed = True
closed_date = <Date 2019-10-08.12:18:12.316>
closer = 'petr.viktorin'
components = ['Interpreter Core']
creation = <Date 2019-09-12.14:04:20.667>
creator = 'dino.viehland'
dependencies = []
files = []
hgrepos = []
issue_num = 38140
keywords = ['patch']
message_count = 9.0
messages = ['352167', '352805', '353089', '353171', '353179', '353191', '353345', '353876', '354195']
nosy_count = 5.0
nosy_names = ['dino.viehland', 'petr.viktorin', 'eric.snow', 'eelizondo', 'shihai1991']
pr_nums = ['16076', '16354']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue38140'
versions = ['Python 3.9']

[DinoV]

This makes it impossible to port certain types to the stable ABI and remove statics from the interpreter.

[DinoV]

New changeset 3368f3c by Dino Viehland (Eddie Elizondo) in branch 'master':
bpo-38140: Make dict and weakref offsets opaque for C heap types (bpo-16076)
3368f3c

[encukou]

Thanks for the feature!
This still needs documentation, however.

[encukou]

New changeset 468f8a6 by Petr Viktorin in branch 'master':
bpo-38140: Document offsets in PyMemberDef (GH-16354)
468f8a6

[shihai1991]

Got an compile error, i have not check the detail for now:

python: Objects/typeobject.c:2867: PyType_FromSpecWithBases: Assertion `memb->type == 19' failed.

i report it in bpo-38273

[encukou]

This line in _tesctcapimodule.c:
{"__dictoffset__", T_PYSSIZET, -sizeof(void*), READONLY},

gives a legitimate-sounding warning on a Windows buildbot:

     d:\buildarea\3.x.ware-win81-release.nondebug\build\modules\_testcapimodule.c(6409): warning C4146: unary minus operator applied to unsigned type, result still unsigned [D:\buildarea\3.x.ware-win81-release.nondebug\build\PCbuild\_testcapi.vcxproj]

[eduardo-elizondo]

Hey Petr, I'll get to document this and fix the windows warning over the weekend. I'll ping you on Github once it's ready

[eduardo-elizondo]

Woops, just realized that you already documented this, thanks! Btw, Victor already merged a fix for the windows compiler warning. This issue can be closed now

[encukou]

Thank you all!