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Removing old buffer support #85275Description
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GitHub fields:
assignee = 'https://github.com/encukou'
closed_at = None
created_at = <Date 2020-06-24.13:43:42.640>
labels = ['expert-C-API', '3.10', '3.11']
title = 'Removing old buffer support'
updated_at = <Date 2021-08-05.08:33:02.859>
user = 'https://github.com/methane' bugs.python.org fields:
activity = <Date 2021-08-05.08:33:02.859>
actor = 'petr.viktorin'
assignee = 'petr.viktorin'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2020-06-24.13:43:42.640>
creator = 'methane'
dependencies = []
files = []
hgrepos = []
issue_num = 41103
keywords = ['patch']
message_count = 12.0
messages = ['372251', '372391', '381854', '381865', '381873', '398459', '398460', '398467', '398476', '398477', '398560', '398974']
nosy_count = 7.0
nosy_names = ['vstinner', 'petr.viktorin', 'methane', 'lukasz.langa', 'hroncok', 'miss-islington', 'tarun.johar']
pr_nums = ['21117', '27437', '27441']
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue41103'
versions = ['Python 3.10', 'Python 3.11'] Linked PRs
Activitymethane commented on Jun 24, 2020 methane commented on Jun 25, 2020 hroncok commented on Nov 25, 2020 vstinner commented on Nov 25, 2020 PyObject_AsCharBuffer() is dangerous: it returns a dangling pointer by design. PyObject_GetBuffer() design is safer: the API ensures that the buffer remains valid until PyBuffer_Release() is called.
PyQt5 was updated to use the safe PyObject_GetBuffer()/PyBuffer_Release(). PyQt4 is no longer updated, that's why I proposed a downstream fix which copy/paste the old code. Changing PyQt4 to use the safe API was not worth it, since it's complex to redesign the impacted function qpycore_encode(). methane commented on Nov 26, 2020 Thank you for reporting. I removed these APIs to get such feedback as early as possible.
We are free to revive these APIs if it breaks too much and some projects can not be fixed before Python 3.10 release.
Some project maintainers ignore deprecations and wait compile errors to fix soemthing. (e.g. rogerbinns/apsw#288 (comment))
That's why we need to break some projects during alpha phase.
What is the benefit of removing this? Is copy pasting the compatibility layer to (possibly many) different projects worth the "cleanup"?
Oh, no need to copy-paste compatibility layer for all projects. They can migrate to new APIs. tarunjohar commented on Jul 29, 2021 Also filed under https://bugs.python.org/issue44609
PEP-384 and PEP-652 define a stable ABI to be used with Python 3.2 and later. On Windows, symbols for the stable ABI are exported from the python3.dll shared library.
The following functions are present in Python 3.9 but have been removed from Python 3.10b3:
PyObject_AsCharBuffer()
PyObject_AsReadBuffer()
PyObject_AsWriteBuffer()
PyObject_CheckReadBuffer() Without these functions, an extension cannot utilize the stable ABI to access the buffer memory of data structures. The buffer protocol is suggested as an alternative, but the buffer functions PyObject_GetBuffer() and PyBuffer_Release() are not present in the stable ABI.
While these two functions may be added to the stable ABI, removal of the four functions above makes Python 3.10 incompatible with previous versions. It is requested that the four functions be reinstated and maintained as described in PEP-652. methane commented on Jul 29, 2021 Oh, I didn't notice that APIs deprecated in Python 3.0 are included in stable ABIs defined at Python 3.2! methane commented on Jul 29, 2021 Should I resurrect only function implementation and symbol?
Or may I resurrect definitions in header files too? vstinner commented on Jun 1, 2023 I closed my issue #105186 as a duplicate of this one. Copy of my message.
Would it be ok to remove the legacy "buffer" API in Python 3.13, scheduled for October 2024? I'm talking about functions:
- PyObject_AsCharBuffer()
- PyObject_CheckReadBuffer()
- PyObject_AsReadBuffer()
- PyObject_AsWriteBuffer()
This API is deprecated since Python 3.0 and is older than the new Py_buffer API. The Py_buffer API is safer: it has a PyBuffer_Release() method to notify when the consumer is done: the resource can be released. The Py_buffer API is now commonly used.
In June 2020, there was a first attempt to remove these functions in issue #85275: commit 6f8a6ee. It caused too many troubles and had to be reverted the following year (commit ce5e1a6, July 2021). The removed functions were still used by at least 6 projects:
The webassets project was also mentioned, but I'm not sure that its failure is related to these removal: see https://bugzilla.redhat.com/show_bug.cgi?id=1899555 I cannot find these functions in https://github.com/Kronuz/pyScss code right now.
Sadly, the 4 functions are part of the stable ABI and have to be kept there. I'm only asking to remove them in the C API. The issue #88775 was complaining that the functions were removed wheareas they are part of the stable ABI. encukou commented on Jun 1, 2023 Sorry I didn't get to this.
Removing them from public API, including the limited API, is AFAIK fine. But
Sadly, the 4 functions are part of the stable ABI and have to be kept there
Please keep (or add) tests for them, so they don't regress. vstinner commented on Jun 1, 2023 I propose to only remove them in the C API, but still export them in the stable ABI. That's what @methane's PR #105137 does. Reacted by Erlend E. Aasland
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