Description

vstinner

opened on Apr 17, 2026

Issue body actions

• Python 3.14 added D and F formats to the ctypes and struct module
• Python 3.15 adds D and F formats to the array module and to memoryview

The D and F formats were chosen for compatibility with numpy. Problem: in fact, numpy uses buffer formats Zd and Zf. Example:

>>> import numpy as np
>>> memoryview(np.array([1, 2, 3], dtype='F')).format
'Zf'
>>> memoryview(np.array([1, 2, 3], dtype='D')).format
'Zd'

So I propose adding support for Zd and Zf formats in array, ctypes, memoryview and struct. It requires changing the code expecting a single character to now accept a string (Zd and Zf have 2 characters!).

Linked PRs

• gh-148675: Add Zd/Zf formats to array, ctypes, memoryview, struct #148676
• gh-148675: Revert GH-146237 and GH-146241 #148674
• gh-148675: Remove F and D formats from array and memoryview #149368
• gh-148675: Optimize arraydescr structure: use char[3] #149455
• gh-148675: Use a string for ctypes cparam tag #149778
• gh-148675: Reuse typecodes for array.array() error message #149779
• [3.15] gh-148675: Use a string for ctypes cparam tag (GH-149778) #149869

Activity

1. vstinner

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Apr 17, 2026
2. vstinner

   added 2 commits that reference this issue on Apr 17, 2026

   pythongh-148675: Add Zd/Zf formats to array, ctypes, memoryview, struct

   fcd568f

   pythongh-148675: Add Zd/Zf formats to array, ctypes, memoryview, struct

   d50838d
3. vstinner commented on Apr 17, 2026

   

   vstinner

   on Apr 17, 2026

   MemberAuthor

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   This issue was escalated to the Steering Council: Decide buffer protocol format string for complex numbers.
4. skirpichev commented on Apr 17, 2026

   

   skirpichev

   on Apr 17, 2026

   Member

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   The D and F formats were chosen for #132827. Problem: in fact, numpy uses buffer formats Zd and Zf.

   In fact, numpy uses both. So, 'F'/'D' codes does make sense for the ctypes module, at least. If SC approves the compatibility break - we can change buffer formats to Zd/Zf in the ctypes module.

   So I propose adding support for Zd and Zf formats in array, ctypes, memoryview and struct. It requires changing the code expecting a single character to now accept a string (Zd and Zf have 2 characters!).

   I think it's better to revert changes for array and memoryview (#148674) and leave problem for a new champion, who will make a PEP with a proper extension of the struct format string for new types.

   Reacted by Petr Viktorin
5. StanFromIreland

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on Apr 17, 2026
6. encukou

   added

   release-blocker

   on May 4, 2026
7. github-project-automation

   added this to Release and Deferred blockers 🚫on May 4, 2026
8. github-project-automation

   moved this to Todo in Release and Deferred blockers 🚫on May 4, 2026
9. vstinner

   added 2 commits that reference this issue on May 4, 2026

   gh-148675: Add Zd/Zf formats to array, ctypes, memoryview, struct (#1…

   6e6f905

   pythongh-148675: Remove F and D formats from array and memoryview

   80fe449
10. encukou

    added a commit that references this issue on May 4, 2026

    gh-148675: Remove F and D formats from array and memoryview (GH-149368)

    5dd5c8b
11. hugovk commented on May 4, 2026

    

    hugovk

    on May 4, 2026

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    Are we all done here for 3.15?
12. encukou commented on May 5, 2026

    

    encukou

    on May 5, 2026

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    For b1, yes. The Steering Council will need to discuss this, later.

    Reacted by Hugo van Kemenade
13. encukou

    removed

    release-blocker

    on May 5, 2026
14. 9 remaining items
15. scoder

    added 4 commits that reference this issue on May 7, 2026

    Warn about C API/ABI instability in array.array docs (GH-7669)

    df942af

    Adapt array module declarations Python 3.15 changes (GH-7659)

    8885de1

    Adapt array module declarations Python 3.15 changes (GH-7659)

    a470483

    Warn about C API/ABI instability in array.array docs (GH-7669)

    d234073
16. vstinner

    added 4 commits that reference this issue on May 13, 2026

    pythongh-148675: Use a string for ctypes cparam tag

    f40bea4

    gh-148675: Reuse typecodes for array.array() error message (#149779)

    a8ef467

    gh-148675: Use a string for ctypes cparam tag (#149778)

    3ecca22

    [3.15] gh-148675: Use a string for ctypes cparam tag (GH-149778) (#14…

    cc624f7
17. vstinner commented on May 18, 2026

    

    vstinner

    on May 18, 2026

    MemberAuthor

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    Add support for numpy buffer format Zf and Zd

    The initial issue has been implemented. For further work, please open new issue. I close this one.
18. vstinner

    closed this as completedon May 18, 2026
19. github-project-automation

    moved this from Todo to Done in Release and Deferred blockers 🚫on May 18, 2026
20. serge-sans-paille

    added 4 commits that reference this issue on May 30, 2026

    Fix typing of array.typecodes for Python 3.15

    1c51239

    Fix typing of array.typecodes for Python 3.15

    800028b

    Fix typing of array.typecodes for Python 3.15

    abbfde1

    Fix typing of array.typecodes for Python 3.15

    1165bb0

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