Mailman 3 November 2021 - capi-sig

New script: add Python 3.10 support to your C extensions without losing Python 3.6 support
by Victor Stinner 07 May '22

07 May '22

Hi, I wrote a new script which adds Python 3.10 support to your C extensions without losing Python 3.6 support: https://github.com/pythoncapi/pythoncapi_compat For example, it replaces "op->ob_type" with "Py_TYPE(op)" and replaces "frame->f_back" with "_PyFrame_GetBackBorrow(frame)". It relies on the pythoncapi_compat.h header file that I wrote to implement Python 3.9 and Python 3.10 on old Python versions. Examples: Py_NewRef() and PyThreadState_GetFrame(). The _PyFrame_GetBackBorrow() function doesn't exist in the Python C API, it's only provided by pythoncapi_compat.h to ease the migration of C extensions. I advise you to replace _PyFrame_GetBackBorrow() (borrowed reference) with PyFrame_GetBack() (strong reference). The PyFrame_GetBack() function was added to Python 3.9 and pythoncapi_compat.h provides it on older Python versions. This project is related to my PEP 620 "Hide implementation details from the C API" which tries to make the C API more abstract to later allow to implement new optimization in CPython and to make other Python implementations like PyPy faster when running C extensions. This project only targets extension modules written in C by using directly the "Python.h" API. I advise you to use Cython or HPy to no longer be bothered with incompatible C API changes at every Python release ;-) * https://cython.org/ * https://hpy.readthedocs.io/ I hope that my script will facilitate migration of C extensions to HPy. Victor -- Night gathers, and now my watch begins. It shall not end until my death.

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ANN: expy 0.6.5 released!
by Yingjie Lan 16 Apr '22

16 Apr '22

EXPY is an express way to extend Python! EXPY provides a way to extend python in an elegant way. For more information and a tutorial, see: http://expy.sourceforge.net/ What's new: 1. Correct treatment of __init__ method. 2. Give warnings of missing Py_INCREF on appropriate special type methods. 3. Documentation update. Cheers, Yingjie

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Deallocating objects from previous run
by Victor Milovanov 31 Mar '22

31 Mar '22

Hi, TL;DR; Is it safe to Py_DecRef an object that was created before Py_Finalize after Py_Initialize was called to restart Python runtime? I am debugging 3.9+ support in https://github.com/pythonnet/pythonnet The issue I originally got is validate_list from gcmodule.c fails at assert(prev == GC_PREV(head)); In debugging this, I sprinkled my code with calls to validate_list, and found that the assertion fails in the following scenario: Py_Initialize(); ... PyObject* myObj = PyObject_Call(simple_class, empty_tuple, NULL); Py_Finalize(); ... Py_Initialize(); ... validate_list(gc.generations[2], collecting_clear_unreachable_clear); // OK Py_DecRef(myObj); validate_list(gc.generations[2], collecting_clear_unreachable_clear); // EXPLOSION Now I have not yet tried to narrow down the steps further, because I realised that I am unsure about the question in TL;DR;. E.g. is this use of myObj supported by embedding API in general, or is this expected, that after reinitializing the runtime Py_DecRef on old objects would break GC? In my scenario simple_class is defined in Python as inheriting from object, and only has two attributes set at runtime. One has value builtins.StopIteration, and the other one is an instance of traceback. Regards, Victor

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ANNOUNCE: PyBindGen 0.8
by Gustavo Carneiro 10 Mar '22

10 Mar '22

The other day I released PyBindGen 0.8. Main news is that it features a new experimental header file scanner based on pygccxml (i.e., it's similar to py++ in scope, if not in maturity, but does not use boost.pythonunderneath). == What == PyBindGen is a Python module that is geared to generating C/C++ code that binds a C/C++ library for Python. It does so without extensive use of either C++ templates or C pre-processor macros. It has modular handling of C/C++ types, and can be easily extended with Python plugins. The generated code is almost as clean as what a human programmer would write, and does not depend on any library or header files besides Python itself. == Where == https://launchpad.net/pybindgen/ == NEWS == - Support C++ instance attributes through getter/setter methods - Support functions as methods of C++ classes - Support the PyObject* type - Support unsigned int, C strings (char*) (from Mark Lee) - Add basic support for enum types - New experimental automatic module generator based on C/C++ header file scanner and annotations in comments, using pygccxml - Some bug fixes -- Gustavo J. A. M. Carneiro INESC Porto, Telecommunications and Multimedia Unit "The universe is always one step beyond logic." -- Frank Herbert

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C API equivalent to abc.ABCMeta.register?
by Daniel Stutzbach 02 Mar '22

02 Mar '22

I'm the author of an extension module (blist) that provides a type that fits the MutableSequence API. Is there a canonical way for me to register the type as a MutableSequence from the C API? -- Daniel Stutzbach, Ph.D. President, Stutzbach Enterprises, LLC <http://stutzbachenterprises.com>

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Software Development - Application Development - Game Development
by Gary 10 Jan '22

10 Jan '22

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Py_TYPE() and Py_SIZE() become static inline functions
by Victor Stinner 29 Nov '21

29 Nov '21

Hi, I converted Py_TYPE() and Py_SIZE() macros to static inline functions in the future Python 3.11. It's a backward incompatible change. For example, "Py_TYPE(obj) = type;" must be replaced with "Py_SET_TYPE(obj, type);". You can use the upgrade_pythoncapi.py script of my pythoncapi_compat project which does these changes for you: you just have to copy pythoncapi_compat.h to your project. This header file provides new C API functions like Py_NewRef() and Py_SET_TYPE() to old Python versions, Python 2.7-3.11. => https://github.com/pythoncapi/pythoncapi_compat I already converted Py_TYPE() and Py_SIZE() macros in Python 3.10, but it broke too many C extensions and so I had to revert the change. In the meanwhile, I updated many C extensions and created the pythoncapi_compat project. For example, Cython and numpy have been updated to use Py_SET_TYPE() and Py_SET_SIZE(). Mercurial and immutables projects now use pythoncapi_compat. I'm interested by feedback on my pythoncapi_compat project ;-) Tell me if you need help to update your project for Python 3.11 C API changes: https://docs.python.org/dev/whatsnew/3.11.html#c-api-changes Victor -- Night gathers, and now my watch begins. It shall not end until my death.

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