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[C API] Add explicit support for Cython to the C API #89410

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[C API] Add explicit support for Cython to the C API#89410
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topic-C-APItype-featureA feature request or enhancement

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@markshannon
markshannon
opened on Sep 20, 2021
BPO 45247
Nosy @scoder, @vstinner, @markshannon, @serhiy-storchaka

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 2021-09-20.10:59:47.125>
labels = ['expert-C-API', 'type-feature']
title = '[C API] Add explicit support for Cython to the C API'
updated_at = <Date 2022-02-23.15:21:36.827>
user = 'https://github.com/markshannon'

bugs.python.org fields:

activity = <Date 2022-02-23.15:21:36.827>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2021-09-20.10:59:47.125>
creator = 'Mark.Shannon'
dependencies = []
files = []
hgrepos = []
issue_num = 45247
keywords = []
message_count = 7.0
messages = ['402224', '403812', '403819', '403821', '403823', '403894', '413804']
nosy_count = 4.0
nosy_names = ['scoder', 'vstinner', 'Mark.Shannon', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45247'
versions = []

Activity

  1. markshannon commented on Sep 20, 2021

    @markshannon
    markshannon
    on Sep 20, 2021
    MemberAuthor

    As the C API has evolved it has grown features in an ad-hoc way, driven by the needs to whoever has bothered to add the code.

    Maybe we should be a bit more principled about this. Specifically we should make sure that there is a well defined interface between CPython and the other major components of the Python ecosystem.
    The obvious places to start are with Cython and Numpy.

    This issue deals specifically with Cython. I will leave it to someone who know more about Numpy to open an issue for Numpy.

    Matching Cython issue: cython/cython#4382

    This issue is an attempt to stop the annual occurrence of bugs like https://bugs.python.org/issue43760#msg393401

  2. markshannon
    added
    topic-C-API
    type-featureA feature request or enhancement
    on Sep 20, 2021

  3. vstinner commented on Oct 13, 2021

    @vstinner
    vstinner
    on Oct 13, 2021
    Member

    We need to add C API to abstract access to structures used by Cython:

  4. vstinner
    changed the title [-]Add explicit support for Cython to the C API.[/-] [+][C API] Add explicit support for Cython to the C API[/+] on Oct 13, 2021

  5. markshannon commented on Oct 13, 2021

    @markshannon
    markshannon
    on Oct 13, 2021
    MemberAuthor

    I disagree. All that is doing is locking in the current poor interface.

    We do need to extend the C API for these uses, yes. But we need an API that addresses Cython's needs directly and at a higher level.

    For example, Cython often wants to insert a frame into the call stack for debugging and introspection.

    Rather than have Cython laboriously create a Python frame with fake code object, etc., it would make much more sense for us to offer an API to insert a "native" frame into the stack and update the line number.

    E.g. something like:

    int PushNativeFrame(const char *filename);
void PopNativeFrame(void);
int CurrentNativeFrame_SetLineNumber(int lineno);

    We might even want to use such an API ourselves in some modules.

  6. vstinner commented on Oct 13, 2021

    @vstinner
    vstinner
    on Oct 13, 2021
    Member

    Rather than have Cython laboriously create a Python frame with fake code object, etc., it would make much more sense for us to offer an API to insert a "native" frame into the stack and update the line number.

    I agree with that.

  7. serhiy-storchaka commented on Oct 13, 2021

    @serhiy-storchaka
    serhiy-storchaka
    on Oct 13, 2021
    Member

    I agree with Mark. Instead of exposing internal details in low-level API we should add more high-level API to satisfy concrete needs. It will give us more freedom of changing internals in future.

  8. vstinner commented on Oct 14, 2021

    @vstinner
    vstinner
    on Oct 14, 2021
    Member

    My first attempt: Add PyThreadState_EnterTracing() and PyThreadState_LeaveTracing()
    #28542

    It adds an abstraction on accesses to PyThreadState.tracing and PyThreadState.cframe.use_tracing members.

  9. vstinner commented on Feb 23, 2022

    @vstinner
    vstinner
    on Feb 23, 2022
    Member

    I created bpo-46836: "[C API] Move PyFrameObject to the internal C API".

  10. ezio-melotti
    transferred this issue fromon Apr 10, 2022

  11. vstinner commented on Dec 20, 2023

    @vstinner
    vstinner
    on Dec 20, 2023
    Member

    I closed #107076 as a duplicate of this issue.

  12. vstinner commented on Oct 9, 2025

    @vstinner
    vstinner
    on Oct 9, 2025
    Member

    See also:

  13. vstinner commented on Oct 9, 2025

    @vstinner
    vstinner
    on Oct 9, 2025
    Member

    @da-woods created a list of Python internals used by Cython in 2022: cython/cython#4635

  14. vstinner
    marked C API: Cython 3.0 uses private functions removed in Python 3.13 (numpy 1.25.1 fails to build) #107076 as a duplicate of this issue on Oct 15, 2025
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