Prepare CPython for opaque PyObject structure.

[WildCard65]

BPO	41188
Nosy	@ronaldoussoren, @vstinner, @WildCard65
PRs	[WIP, DO NOT MERGE] bpo-41188: Prepare CPython for opague PyObject structure. #21262

^{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 2020-07-01.17:43:02.332>
labels = ['interpreter-core', 'expert-C-API', 'type-feature', '3.10']
title = 'Prepare CPython for opaque PyObject structure.'
updated_at = <Date 2020-07-07.19:55:22.137>
user = 'https://github.com/WildCard65'

bugs.python.org fields:

activity = <Date 2020-07-07.19:55:22.137>
actor = 'ronaldoussoren'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core', 'C API']
creation = <Date 2020-07-01.17:43:02.332>
creator = 'WildCard65'
dependencies = []
files = []
hgrepos = []
issue_num = 41188
keywords = ['patch']
message_count = 1.0
messages = ['372775']
nosy_count = 3.0
nosy_names = ['ronaldoussoren', 'vstinner', 'WildCard65']
pr_nums = ['21262']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41188'
versions = ['Python 3.10']

[WildCard65]

The goal of bpo-39573 is to make "PyObject" and opaque structure in the limited API.

To do that, a few mandatory changes will be required to CPython in order to allow for seamless implementation.

Namely:

1. User types need to get away from directly referencing PyObject.

   • This can be done by adding a new variable to "PyTypeObject" who's value is an offset into the object's pointer to the type's internal structure.
     -- Example: 'PyType_Type.tp_obj_offset' would be the value of "sizeof(PyVarObject)".
     -- For custom types with another base: The value would be calculated from the base's "tp_obj_offset" + "tp_basicsize"

2. Create a linkable static library to facility method calls requiring internal implementation.

   • This static library will be implementation defined, IE: using internal methods specific to the runtime that created it.
   • Public facing methods will use generic names for example, "PyObject_GetType" will get the object's ob_type (or whatever the target runtime calls it).

[iritkatriel]

The PR was closed by the OP after a core dev requested changes. So I am assuming the project was abandoned and closing the issue as well.