capi-sig June 2020

capi-sig@python.org

15 participants
12 discussions

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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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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Mail l8st
by casperssidekick 10 Jul '21

10 Jul '21

Sent from my Verizon, Samsung Galaxy smartphone

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Module state access from slot methods: _PyType_GetModuleByDef
by Petr Viktorin 22 Sep '20

22 Sep '20

Hello, Now that PEP 573 (Module State Access from C Extension Methods) is in, it's time to address the most important part missing from it: module state access from slot methods (like tp_init or nb_add). This has long history; see e.g. a thread I started in 2015: https://mail.python.org/pipermail/import-sig/2015-July/thread.html#1037 Most recently, a possible solution, an MRO walker, was one of the last things removed from PEP 573 before acceptance, because the proposed solution was broken: see https://mail.python.org/archives/list/python-dev@python.org/message/PFBAQWQ… Here's the removed text: > Slot methods > ------------ > > To allow access to `per-module state`_ from slot methods, an MRO walker > will be implemented:: > > PyTypeObject *PyType_DefiningTypeFromSlotFunc(PyTypeObject *type, > int slot, void *func) > > The walker will go through bases of heap-allocated ``type`` > and search for class that defines ``func`` at its ``slot``. > > The ``func`` does not need to be inherited by ``type`` (i.e. it may have been > overridden in a subclass). The only requirement for the walker to find the > defining class is that the defining class must be heap-allocated. > > On failure, exception is set and NULL is returned. and the last iteration of the implementation is here: https://github.com/Dormouse759/cpython/blob/41fe314c5124fa9434d56169868dfc0… A MRO walker is not efficient. The other viable options I'm aware of are: - putting a pointer in the class object (which would need reliable class-level storage, see https://mail.python.org/archives/list/capi-sig@python.org/thread/BWVQLET4L3… ) - solutions that aren't fully general, like context variables or putting a pointer in each instance (thorny because constructors/initializers are themselves slots) - "__typeslots__" mentioned in https://mail.python.org/pipermail/import-sig/2015-July/001035.html -- which are, IMO, quite invasive Given that, I believe that some kind of MRO walker is still the best immediate solution, mainly because it's easiest to implement. If done well, it can only use current public API (limiting the maintenance burden you'd have with something wired into the internals, and allowing it to be copied to 3rd party code to support older Python versions), and should be easy to replace with a more performant solution once that comes out. And if it's added, more modules could switch to the stable ABI and eschew process-global state, so we get more exposure and experience with the remaining problems. Now, the main problem with "PyType_DefiningTypeFromSlotFunc" is that it looked slot functions, which can be set from Python code, and doing so can easily introduce C-level failures. To solve this, my next thought is instead looking for something only available in C: the PyModuleDef. Here's an implementation of such an MRO walker, which I call "_PyType_GetModuleByDef": https://github.com/encukou/cpython/blob/98dd889575cf7d1688495983ba791e14894… My thinking is to start using this in 3.10 as internal API to get a feel for its strengths and weaknesses. It should be easy to rewrite the function to only use public API, and added to another project (like Cython). It should also be easy to make it public once we're sure it's the way forward. What are your thoughts?

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PyLong_{As,From}ByteArray
by doodspav＠gmail.com 23 Jun '20

23 Jun '20

Can we make `PyLong_AsByteArray(PyLongObject* v, unsigned char* bytes, size_t n, int little_endian, int is_signed);` and `PyObject * PyLong_FromByteArray(const unsigned char* bytes, size_t n, int little_endian, int is_signed);` available as publicly documented functions? They're already available internally, as can be seen here (https://github.com/python/cpython/blob/578c3955e0222ec7b3146197467fbb0fcfae…) so all that would be required (I think) would be exporting the symbols and updating the documentation (https://docs.python.org/3/c-api/long.html). The benefits would be that we could use this when we want to use fixed width integer types without having to check the width of fundamental integer types (so we could use `int32_t` rather than checking `sizeof(int)` or the corresponding macro). This would also be useful if someone wanted to use compiler extension fixed width types such as `__int128_t` (and the corresponding unsigned version).

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gcc -DPy_NO_DEPRECATED_API option?
by Barry Scott 19 Jun '20

19 Jun '20

I have been following the discussions on removing deprecated macros and functions from the C API. I checked my code, PyCXX and have a coupld of issues that is easy to fix. But I may have missed something. What would help me is to be able to build extensions with all the deprecated pieces of the C API removed. A bit like the way the limited C API works via the -DPy_LIMITED_API=0x03040000 option. What do you think? Barry

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Re: [Python-Dev] Removal of _Py_ForgetReference from public header in 3.9 issue
by Petr Viktorin 16 Jun '20

16 Jun '20

On 2020-06-14 22:10, cpython(a)nicwatson.org wrote: > Please excuse if this is the wrong mailing list. I couldn't find one for module maintainers. This is relevant to capi-sig(a)python.org; let's continue here. > I maintain an open source Python module in C. I'm trying to verify for the first time that the module still works with cpython 3.9. This module does *not* use the "limited" C API. > > In building my module against 3.9b3, I'm getting a missing declaration warning on _Py_ForgetReference. My module builds and passes test fine, this is just a compiler warning issue. What does the _Py_ForgetReference function do? The [documentation] says it's only for use in the interpereter core, so I'd assume it's . [documentation]: https://docs.python.org/3/c-api/refcounting.html > The change that caused this was made in: > > commit f58bd7c1693fe041f7296a5778d0a11287895648 > Author: Victor Stinner <vstinner(a)python.org> > Date: Wed Feb 5 13:12:19 2020 +0100 > > bpo-39542: Make PyObject_INIT() opaque in limited C API (GH-18363) > ... > > I definitely need the _Py_ForgetReference call for a particularly hairy error condition (https://github.com/jnwatson/py-lmdb/blob/master/lmdb/cpython.c#L888 if you're curious). In fact, my tests will seg fault if I don't have that call and trace refs is enabled. I can't follow the reasoning behind the code easily. Why do you use _Py_ForgetReference and PyObject_Del, instead of Py_DECREF(self)? > Should I put an #ifdef Py_TRACE_REFS around the call? Ignore it? What do you think is the proper resolution?

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Instantiation of subclasses of ctypes
by Justin Capella 15 Jun '20

15 Jun '20

The Structure interface of ctypes is intended to be subclassed yet the subclasses init and new aren't invoked. I think this was intended as an optimization but it is inconsistent and confusing. The only documentation about this behavior takes the form of a unit test, which may not have ever worked properly. There is an issue about this open here https://bugs.python.org/issue38860 I'm of the opinion it should not be "special", what does the community think?

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capi-sig June 2020