Mailman 3 February 2010 - capi-sig

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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Re: [capi-sig] (no subject)
by Hrvoje Niksic 01 Mar '10

01 Mar '10

"Goudar, Girish" <Girish.Goudar(a)goodrich.com> writes: > Thanks for the quick reply. I can use the struct module at Python side > and use the pack() function to pack the data. But in the DEOS side I > need to unpack the data for that I need to use unpack() function. But > DEOS is not supporting unpack() function. What to do? I meant to use that you can use struct.pack to create data that can be interpreted as a structure defined in C, assuming the same architecture is run on both machines. Such sharing of data is one of the use cases of the struct module. For example: # python side: import struct s = struct.pack('cid', 'A', 10, 20.0) send_data_to_network(s) /* C side: */ struct data_desc { char c; int i; double d; }; char *s; struct data_desc data; s = read_data_from_network(); memcpy(&data, s, sizeof(data)); /* data.c is now the char data.i the int data.d the float (double) */

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Re: [capi-sig] (no subject)
by Hrvoje Niksic 24 Feb '10

24 Feb '10

"Goudar, Girish" <Girish.Goudar(a)goodrich.com> writes: > I want to pass a structure (which contains int, float, char etc) from > a client program written in Python to a server program written in C > (Operating system is DEOS). But the "socket.send" command in Python > supports only String or Readonly buffer. I want to pass a structure. > Could you please help me on this? Aside from the remark brought up by Stefan, I'd recommend the use of the "struct" module.

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Re: [capi-sig] (no subject)
by Stefan Behnel 24 Feb '10

24 Feb '10

Goudar, Girish, 24.02.2010 11:13: > I want to pass a structure (which contains int, float, char etc) from a > client program written in Python to a server program written in C > (Operating system is DEOS). But the "socket.send" command in Python > supports only String or Readonly buffer. I want to pass a structure. > Could you please help me on this? This has nothing to do with the Python C-API (so this is the wrong list to ask this on). What you have to do is figure out the structure of the data stream that the server requires, and then send your data in that structure. Stefan

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(no subject)
by Goudar, Girish 24 Feb '10

24 Feb '10

Hi All, I want to pass a structure (which contains int, float, char etc) from a client program written in Python to a server program written in C (Operating system is DEOS). But the "socket.send" command in Python supports only String or Readonly buffer. I want to pass a structure. Could you please help me on this? Thanks and Regards, Girish P.G

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varargs in the C API.
by Guillaume Yziquel 19 Feb '10

19 Feb '10

Hello. I've been trying to wrap up the C functions that have an ellipsis, or a vararg, such as PyTuple_Pack. I tried to use avcall.h to pass a dynamically-determined number of arguments to the underlying function. Having a hard time: > ocaml -init ocamlinit > Objective Caml version 3.11.1 > > # let x = ((Python.of_int 6) :> Python.obj);; > val x : Python.obj = <abstr> > # let y = ((Python.of_int 4) :> Python.obj);; > val y : Python.obj = <abstr> > # let args = Python.tuple_pack [x; y];; > [seldon:09731] *** Process received signal *** > [seldon:09731] Signal: Segmentation fault (11) > [seldon:09731] Signal code: Address not mapped (1) > [seldon:09731] Failing at address: 0x5 > [seldon:09731] [ 0] /lib/libpthread.so.0 [0x2b9099aca990] > [seldon:09731] [ 1] /usr/lib/libavcall.so(__builtin_avcall+0x2a5) [0x2b909a14c905] > [seldon:09731] *** End of error message *** > make: *** [test] Erreur de segmentation So just wondering: has anyone succeeded in wrapping functions like PyTuple_Pack using stuff like avcall, libffi, or cinvoke? Here's the code of my wrapper: > CAMLprim value ocamlpython_py_tuple_pack (value ml_len, value ml_pyobjs) { > > av_alist argList; > PyObject * retVal; > av_start_ptr(argList, PyTuple_Pack, PyObject*, retVal); > > #if defined(__s390__) || defined(__hppa__) || defined(__cris__) > #define av_Py_ssize_t av_long > #else > #define av_Py_ssize_t av_int > #endif > > av_Py_ssize_t(argList, Pyoffset_val(ml_len)); > while (ml_pyobjs != Val_emptylist) { > av_ptr(argList, PyObject*, Pyobj_val(Field(ml_pyobjs, 0))); > ml_pyobjs = Field(ml_pyobjs, 1); > } > > av_call(argList); > return(Val_owned_pyobj(retVal)); > } Please tell me if you see something fishy that my eyes do not catch. -- Guillaume Yziquel http://yziquel.homelinux.org/

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How to inspect module objects.
by Guillaume Yziquel 15 Feb '10

15 Feb '10

Hello. I'm currently reworking the existing software embedding Python (v2.5 for now) into Objective Caml. You can already do some trivial things with it: > yziquel@seldon:~$ ocaml > Objective Caml version 3.11.1 > > # #use "topfind";; > - : unit = () > Findlib has been successfully loaded. Additional directives: > #require "package";; to load a package > #list;; to list the available packages > #camlp4o;; to load camlp4 (standard syntax) > #camlp4r;; to load camlp4 (revised syntax) > #predicates "p,q,...";; to set these predicates > Topfind.reset();; to force that packages will be reloaded > #thread;; to enable threads > > - : unit = () > # #require "python.interpreter";; > /usr/lib/ocaml/python: added to search path > /usr/lib/ocaml/python/python.cma: loaded > /usr/lib/ocaml/python/oCamlPython.cmo: loaded > # let q = Python.Module.import "dolfin";; > val q : Python.obj = <abstr> > # let w = Python.Module.import "modulethatdoesnotexist";; > Exception: Python.Exception.Python_failure <abstr>. > # So it catches exceptions when trying to import a module that does not exist, and it succeeds when importing dolfin, a module that does exist on my box. But then I'd like to inspect the contet of this module. So, here's my question: How do you access the content of this module, or the content of the python object, preferably with the C API. All apologies if these questions seem trivial to you, but I'm quite new to python and its internals. Pointers to relevant (tutorial?) documentation are appreciated. All the best, -- Guillaume Yziquel http://yziquel.homelinux.org/

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expy 0.6 released
by Yingjie Lan 10 Feb '10

10 Feb '10

Hi: EXPY (http://expy.sourceforge.net/) is an express way to extend Python. Why consider expy? Here are some good reasons: (I). WYSIWYG. The expy project enables you to write your module in Python the way your extension would be (WYSIWYG), and meanwhile write your implementation in pure C. You specify your modules, functions, methods, classes, and even their documentations the usual way of writing your Python correspondences. Then provide your implementation to the functions/methods by returning a multi-line string. By such an arrangement, everything falls in its right place, and your extension code becomes easy to read and maintain. Also, the generated code is very human-friendly. (II). You only provide minimal information to indicate your intension of how your module/class would function in Python. So your extension is largely independent from the Python extension API. As your interaction with the Python extension API is reduced to minimal (you only care about the functionality and logic), it is then possible that your module written in expy can be independent of changes in the extension API. (III). The building and setup of your project can be automatically done with the distutil tool. In the tutorial, there are ample examples on how easily this is achieved. (IV). Very light weight. The expy tool is surprisingly light weight dispite of its powerful ability, as it is written in pure Python. There is no parser or compiler for code generation, but rather the powerful reflexion mechanism of Python is exploited in a clever way to generate human-friendly codes. Currently, generating code in C is supported, however, the implementation is well modularized and code generation in other languages such as Java and C++ should be easy. Currently, EXPY/CXPY works with Python 2.5, 2.6. I haven’t tested with Python 2.7 or 3.x (for 3.x, need to use the code tool first, and I am not sure if the C API for 3.x has changed much, if you happen to try it out, let me know what happened). While there are already a couple of other projects trying to simply this task with different strategies, such as Cython, Pyrex and modulator, this project is unique and charming in its own way. All you need is the WYSIWYG Python file for your module extension, then expy takes care of everything else. What follows in this documentation is on how to extend Python in C using expy-cxpy: the module expy helps define your module, while module cxpy helps generate C codes for your defined module. Yingjie

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ANN: PyBindGen 0.14
by Gustavo Carneiro 07 Feb '10

07 Feb '10

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. It can be downloaded from: http://code.google.com/p/pybindgen/ Bug reports should be filed here: https://bugs.launchpad.net/ <https://bugs.launchpad.net/pybindgen> pybindgen <https://bugs.launchpad.net/pybindgen> <https://bugs.launchpad.net/pybindgen>Documentation: http://packages.python.org/PyBindGen/ NEWS: === pybindgen 0.14 === - Multiple inheritance support - Virtual methods can now be overridden with Method instead of _Method - Add annotation support for instance attributes - Benchmarks (vs Boost.Python, SWIG, and SIP) - New types supported: int16_t& and std::string* parameter types - Non-virtual protected methods are now also wrapped - Wrap enum pointer params Note: this release marks the beginning of a transition to a minor change in the API of the generated bindings. Prior to PyBindGen version 0.14, the code generated to handle C++ virtual methods required Python user code to define a _foo method in order to implement the virtual method foo. Since 0.14, PyBindGen changed so that virtual method foo is implemented in Python by defining a method foo, i.e. no underscore prefix is needed anymore. Setting pybindgen.settings.deprecated_virtuals to True will force the old virtual method behaviour. But this is really deprecated; newer code should set pybindgen.settings.deprecated_virtuals to False. In PyBindGen 0.14, if the option pybindgen.settings.deprecated_virtuals is not set, PyBindGen emits a warning and assumes the value of True in order to preserve backward compatibility. In PyBindGen 0.15, the default value of this option will change to False, and in 0.16 the support for deprecated virtuals will be removed. This change was made to make the user code interface more intuitive, and to align it with other Python bindings tools such as SIP, Boost.Python, and SWIG. -- Gustavo J. A. M. Carneiro INESC Porto, UTM, WiN, http://win.inescporto.pt/gjc "The universe is always one step beyond logic." -- Frank Herbert

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expy 0.5.2 released
by Yingjie Lan 03 Feb '10

03 Feb '10

Hi, expy is an expressway to extend python. in release 0.5.2, expy now supports custom exceptions, besides all built-in ones, and exception handling is made easy. for more info, see http://expy.sourceforge.net/ cheers, Yingjie

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Python 3.x PyObject_HEAD versus PyObject_VAR_HEAD
by Philip Semanchuk 02 Feb '10

02 Feb '10

Hi all, I'm trying to port my posix_ipc extension to Python 3, and I'm confused by the documentation for PyObject_HEAD and PyObject_VAR_HEAD. My understanding is that a PyObject-derived type should begin its PyTypeObject struct with PyObject_HEAD and a PyVarObject-derived type with PyObject_VAR_HEAD. the documentation says of PyVarObject, "This type does not often appear in the Python/C API." http://docs.python.org/3.1/c-api/structures.html#PyVarObject The doc also says that PyObject_VAR_HEAD, "is used when declaring new types which represent objects with a length that varies from instance to instance." http://docs.python.org/3.1/c-api/structures.html#PyObject_VAR_HEAD I assumed, then, that PyObject_VAR_HEAD would also appear infrequently, but that's not the case at all. In fact, I can't find PyObject_HEAD used at all in the Python 3.1.1 source code, whereas PyObject_VAR_HEAD is used hundreds of times, including for objects that don't have a length (like the float type, for instance). Is the documentation wrong, or am I misreading it? Suggestions appreciated. THanks Philip

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expy 0.5.1 released
by Yingjie Lan 01 Feb '10

01 Feb '10

Hi there, EXPY 0.5.1 released, the exception raising feature is enhanced so that you can raise any builtin exceptions. Custom exceptions will be supported soon. For more information, see http://expy.sourceforge.net/ EXPY is an expressway to extend Python! Regards, Yingjie

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