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gh-112015: Implement `ctypes.memoryview_at()` by rianhunter · Pull Request #112018 · python/cpython · GitHub

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gh-112015: Implement ctypes.memoryview_at() - #112018

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encukou merged 25 commits into
python:mainfrom
rianhunter:ctypes-buffer-at
Jan 3, 2025
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gh-112015: Implement ctypes.memoryview_at()#112018
encukou merged 25 commits into
python:mainfrom
rianhunter:ctypes-buffer-at

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rianhunter commented Nov 13, 2023 •
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ctypes currently has no way to easily create a buffer object from a pointer and a dynamic size. It is possible to create memoryview objects of array objects that refer to existing memory (e.g.
memoryview((c_byte * size).from_address(address))) but this is inefficient and the resulting memoryview object doesn't allow editing via python (invalid format errors are thrown, this is due to how ctypes objects implements the buffer protocol).

ctypes.memoryview_at() fills that gap in the API. This is similar to ffi.buffer() in the cffi module.

Fixes #112015

📚 Documentation preview 📚: https://cpython-previews--112018.org.readthedocs.build/

Implement ctypes.buffer_at()
236657b 
ctypes currently has no way to easily create a buffer object
from a pointer and a dynamic size. It is possible to create
memoryview objects of array objects (e.g.
memoryview((c_ubyte * 10)())) but this is excessively slow when
implementing a callback function in Python that is passed a
dynamic void * and a size_t.

`ctypes.buffer_at()` fills that gap in the API. This is similar
to `ffi.buffer()` in the cffi module.
rianhunter changed the title Implement ctypes.buffer_at() gh-112015: Implement ctypes.buffer_at() Nov 13, 2023
bedevere-app Bot mentioned this pull request Nov 13, 2023
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serhiy-storchaka reviewed Jan 18, 2024
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Comment thread Modules/_ctypes/_ctypes.c Outdated
serhiy-storchaka reviewed Jan 18, 2024
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Please add tests and What's New entry.

And I think that it is worth to support large buffers.

Comment thread Modules/_ctypes/_ctypes.c Outdated
Comment thread Doc/library/ctypes.rst Outdated
Comment thread Doc/library/ctypes.rst Outdated
Comment thread Misc/NEWS.d/next/Library/2023-11-12-21-53-40.gh-issue-112015.2WPRxE.rst Outdated
Comment thread Misc/NEWS.d/next/Library/2023-11-12-21-53-40.gh-issue-112015.2WPRxE.rst Outdated
Comment thread Doc/library/ctypes.rst
rianhunter and others added 6 commits January 18, 2024 14:14
Apply suggestions from code review
00e3c23 
Documentation improvements

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Make size argument a Py_ssize_t, per @serhiy-storchaka suggestion
df0f992
Add what's new entry
eaa2d13
Rename buffer_at to memoryview_at
db3a26a 
It's a more descriptive and precise name.
Make mutable objects the default
d7e2f25 
It's more common that the user will want a memoryview object that can
be mutated. An immutable object is more rare, so make the default case
return a mutable object.
Add test for ctypes.memoryview_at
097a41c

rianhunter commented Jan 19, 2024

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When merging, just flatten all the commits down to a single commit.

rianhunter changed the title gh-112015: Implement ctypes.buffer_at() gh-112015: Implement ctypes.memoryview_at() Jan 19, 2024
encukou reviewed Sep 18, 2024
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Comment thread Lib/test/test_ctypes/test_memfunctions.py Outdated

rianhunter commented Sep 19, 2024

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Abandoned

rianhunter closed this Sep 19, 2024

encukou commented Sep 26, 2024

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I'm sorry but I no longer have time to work on this patch.

No worries. Thank you for your work so far!
I hope you won't mind if I take over and finish it.

encukou reopened this Sep 26, 2024

rianhunter commented Sep 26, 2024

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No problem, feel free

encukou commented Nov 29, 2024

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OK. I went back to the string_at mechanism of calling the C code via ctypes, as the conversion to c_void_p is much more flexible.

encukou commented Dec 16, 2024 •
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Does this look interesting to you, @ZeroIntensity or @picnixz?

picnixz self-requested a review December 16, 2024 17:25
picnixz reviewed Dec 16, 2024
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Comment thread Doc/whatsnew/3.14.rst Outdated
Comment thread Doc/whatsnew/3.14.rst
Comment thread Lib/ctypes/__init__.py
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Comment thread Lib/ctypes/__init__.py Outdated
Comment thread Misc/NEWS.d/next/Library/2023-11-12-21-53-40.gh-issue-112015.2WPRxE.rst
Comment thread Modules/_ctypes/_ctypes.c Outdated

ZeroIntensity commented Dec 16, 2024

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I'll review sometime soon (today or in the next few days).

encukou and others added 3 commits December 19, 2024 14:33
Apply suggestions from code review
5600cef 
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Avoid extra variable
c3c9e17
Merge in the main branch
d1ca15d
ZeroIntensity reviewed Dec 19, 2024
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Mostly LGTM

Comment thread Modules/_ctypes/_ctypes.c
Comment thread Modules/_ctypes/_ctypes.c
Comment thread Lib/test/test_ctypes/test_memfunctions.py Outdated
ZeroIntensity reviewed Dec 20, 2024
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Comment thread Lib/test/test_ctypes/test_memfunctions.py Outdated
ZeroIntensity approved these changes Jan 2, 2025
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I'm happy with this!

encukou merged commit b4f799b into python:main Jan 3, 2025
WolframAlph pushed a commit to WolframAlph/cpython that referenced this pull request Jan 4, 2025
pythongh-112015: Implement ctypes.memoryview_at() (pythonGH-112018)
b3d84e3 
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
srinivasreddy pushed a commit to srinivasreddy/cpython that referenced this pull request Jan 8, 2025
pythongh-112015: Implement ctypes.memoryview_at() (pythonGH-112018)
8f2cce6 
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
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Provide ctypes.memoryview_at()

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