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gh-57060: populate Py_buffer strides field for ctypes arrays. - #4714

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vanossj:fix-issue-12851
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gh-57060: populate Py_buffer strides field for ctypes arrays.#4714
vanossj wants to merge 6 commits into
python:mainfrom
vanossj:fix-issue-12851

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@vanossj

@vanossj vanossj commented Dec 5, 2017 •
edited by serhiy-storchaka
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bpo-12851: populate Py_buffer strides field for ctypes arrays.

PEP 3118 specifies that if PyBUF_STIDES is set in the flags argument for PyCData_NewGetBuffer,

The returned buffer must provide strides information (i.e. the strides cannot be NULL).

However it also says that the strides field of Py_buffer:

...will be filled with a pointer to an array of Py_ssize_t of length ndims (or NULL if ndims is 0)

This patch follows the latter, setting strides for ctypes arrays (ndim>0) but not for other ctypes types

https://bugs.python.org/issue12851

@the-knights-who-say-ni

the-knights-who-say-ni commented Dec 5, 2017

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Hello, and thanks for your contribution!

I'm a bot set up to make sure that the project can legally accept your contribution by verifying you have signed the PSF contributor agreement (CLA).

Unfortunately our records indicate you have not signed the CLA. For legal reasons we need you to sign this before we can look at your contribution. Please follow the steps outlined in the CPython devguide to rectify this issue.

Thanks again to your contribution and we look forward to looking at it!

@vanossj vanossj changed the title Fix issue 12851 bpo-12851: populate Py_buffer strides field for ctypes arrays. Dec 5, 2017
@vanossj

vanossj commented Apr 9, 2018

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@skrah would you be willing to review these changes? Thanks.

MaxwellDupre
MaxwellDupre approved these changes Mar 29, 2022
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Ran ok:
Ran 3 tests in 0.002s
OK

@skrah skrah mannequin mentioned this pull request Apr 10, 2022
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github-actions Bot commented Aug 13, 2022

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This PR is stale because it has been open for 30 days with no activity.

@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label Aug 13, 2022
@serhiy-storchaka
Merge remote-tracking branch 'upstream/main' into fix-issue-12851
41371ae 
# Conflicts:
#	Lib/test/test_ctypes/test_pep3118.py
#	Modules/_ctypes/_ctypes.c
#	Modules/_ctypes/_ctypes_test.c
#	Modules/_ctypes/ctypes.h
#	Modules/_ctypes/stgdict.c
@serhiy-storchaka
Do not report ndim > 1 without the shape
f6be10a 
PyBUF_SIMPLE requests crashed on a multidimensional array: ndim > 1
implies shape != NULL (see PyBuffer_IsContiguous()).  The buffer is C
contiguous, so it can be exposed as flat.

Also, only a multidimensional array is not Fortran contiguous, and
BufferError is more appropriate than TypeError.

Clear the strides when the shape which they point into is freed.
@serhiy-storchaka
Use _testbuffer instead of a new helper in _ctypes_test
03b0de1 
_testbuffer.ndarray already exposes the raw Py_buffer, and it can also
request particular flags, which the buffer_info() helper could not.
@serhiy-storchaka
Rename the NEWS entry to the GitHub issue and describe the change
57c2e6d
@serhiy-storchaka serhiy-storchaka removed the stale Stale PR or inactive for long period of time. label Aug 11, 2026
@serhiy-storchaka

serhiy-storchaka commented Aug 11, 2026

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I have merged the current main into this and made a few changes on top:

  • PyBUF_SIMPLE requests crashed on a multidimensional array — ndim > 1 implies shape != NULL, so it is now exposed as flat.
  • The tests use _testbuffer.ndarray instead of a new helper in _ctypes_test; it can also request particular flags.
  • The NEWS entry was renamed to the GitHub issue number.

Thank you for the patch, and sorry that it took so long.

@serhiy-storchaka serhiy-storchaka changed the title bpo-12851: populate Py_buffer strides field for ctypes arrays. gh-57060: populate Py_buffer strides field for ctypes arrays. Aug 12, 2026
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@vanossj @the-knights-who-say-ni @serhiy-storchaka @MaxwellDupre @ezio-melotti @bedevere-bot