Mailman 3 May 2010 - capi-sig

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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Re: [capi-sig] Python to Scheme type conversion in C?
by Stefan Behnel 31 May '10

31 May '10

[please always reply to the list] Jason Baker, 31.05.2010 21:45: > On Mon, May 31, 2010 at 2:05 PM, Stefan Behnel wrote: >> Jason Baker, 31.05.2010 18:15: >>> >>> I'm working on a Python-to-mzscheme binding using mzscheme's ffi >>> library (mzscheme's rough equivalent of the Python ctypes library). Since you didn't provide the link (and "mzscheme ffi" doesn't get me anything that looks right at first sight), am I right in guessing that you might be referring to this? http://download.plt-scheme.org/doc/351/html/foreign/ >>> I'm looking for a way to convert Python objects into Scheme values. >>> Essentially what I'm trying to do is say "Is this a Python integer? >>> Ok, convert it to a Scheme integer." or "Is this a Python string? >>> Ok, convert it into a Scheme string." ... etc. >>> >>> What is the best way to do this? My first intuition was to call >>> Py*_Check to determine the type, but it turns out that's a macro that >>> can't be used in non-c code. I'm sure I could translate that into the >>> appropriate C code, but that gives me a bad feeling. >> >> Those are macros because that makes them really, really fast, especially in >> Py3. However, their definition changes between Python versions, so replacing >> them by regular C code is really not a good idea. >> >> In general, I wouldn't try to make the wrapper too generic. You might want >> to inspect the underlying Scheme code (potentially at runtime), and infer >> the possible types (or the required conversion) from that. > > Perhaps I should clarify. For now, I'm just trying to embed the python > interpreter in Scheme. Thus, I know what types the scheme values are, > and I know how to translate them into the appropriate Python values. > What I'm trying to figure out is how to go the other way. That is, > how do I figure out what type a PyObject is so I know how to create > the appropriate Scheme value? Why not write a type checking cascade in plain C or Cython? >>> Right now, I'm >>> looking for simple and easy more than efficient and complete (but I >>> would also like to know what the efficient and complete approach would >>> be). >> >> Have you considered integrating this with Cython via a thin C bridge, >> instead of talking to Python's C-API directly? Without knowing anything >> about the FFI you are using here, I suspect that it likely wouldn't be a >> generic wrapper in that case. Instead, it would allow users to write >> specialised and well optimised Scheme wrappers for their specific use case. >> So far, Cython supports calling into C, C++ and Fortran, where the Fortran >> wrapper is also implemented as a C-bridge (via fwrap). A similar Scheme >> binding would allow users to take advantage of Cython's static typing >> features, so that your code wouldn't have to guess types in the first place. > > While I'm sure this approach works for C, C++, and Fortran, I'm afraid > I don't see how this would apply to Scheme. Scheme is a dynamically > typed language just like Python. Why do I want a layer of static > typing in between two dynamically typed languages? Scheme is a strictly typed language, though, and your Scheme code won't run with (or even accept) arbitrary Python input value types, just like your Python code won't run with arbitrary Scheme value types as input. So you have to draw the line somewhere. And since you are using an FFI, which, I assume, passes through C anyway, you might just as well restrict your glue code to suitable types. Stefan

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Python to Scheme type conversion in C?
by Jason Baker 31 May '10

31 May '10

I'm working on a Python-to-mzscheme binding using mzscheme's ffi library (mzscheme's rough equivalent of the Python ctypes library). I'm looking for a way to convert Python objects into Scheme values. Essentially what I'm trying to do is say "Is this a Python integer? Ok, convert it to a Scheme integer." or "Is this a Python string? Ok, convert it into a Scheme string." ... etc. What is the best way to do this? My first intuition was to call Py*_Check to determine the type, but it turns out that's a macro that can't be used in non-c code. I'm sure I could translate that into the appropriate C code, but that gives me a bad feeling. Right now, I'm looking for simple and easy more than efficient and complete (but I would also like to know what the efficient and complete approach would be). Can anyone tell me what the best way to tackle this problem is?

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Easy way to Return Value from 1 line of Embedded Python?
by Jerry Krinock 31 May '10

31 May '10

In a C program I need to unpickle a Python pickle which is generated by someone's Python program. A Python newbie, I was able to do this, but only by writing a little python script file and loading it as a module. But reading from a script file is fragile, has lots of possible errors to handle as you can see below, and is silly since there's only one line of Python. I'd therefore like to create the Python module from a string constant, as with PyRun_SimpleString(), instead of reading a file. But I can't find a function like that which returns a value. Or I just don't know how. Certainly there must be a simpler way to do this... Thank you, Jerry Krinock ***** somePython.py ***************************** #!/usr/bin/env python from pickle import loads def unpickle(x): return loads(x) ***** My C "Proof of Concept" Function ********** #include <Python/Python.h> // Running on Mac OS X char* PythonUnpickle(char* pickle) { PyObject *pName, *pModule, *pFunc; PyObject *pArgs, *pValue; char* unpickledString = NULL ; Py_Initialize(); PyRun_SimpleString("import sys"); PyRun_SimpleString("sys.path.append(\"/Users/jk/Documents/Programming/Python/\")"); pName = PyString_FromString("somePython"); pModule = PyImport_Import(pName); Py_DECREF(pName); if (pModule != NULL) { pFunc = PyObject_GetAttrString(pModule, "unpickle"); /* pFunc is a new reference */ if (pFunc && PyCallable_Check(pFunc)) { pArgs = PyTuple_New(1); // Create the argument to unpickle() pValue = PyString_FromString(pickle); if (!pValue) { Py_DECREF(pArgs); Py_DECREF(pModule); fprintf(stderr, "Cannot convert argument\n"); return NULL ; } // Set the argument into the pArgs tuple PyTuple_SetItem(pArgs, 0, pValue); // Run the python unpickle() function, get result pValue pValue = PyObject_CallObject(pFunc, pArgs) ; Py_DECREF(pArgs) ; // Convert the Python string pValue to a C string if (pValue != NULL) { unpickledString = PyString_AsString(pValue) ; Py_DECREF(pValue); } else { Py_DECREF(pFunc); Py_DECREF(pModule); PyErr_Print(); fprintf(stderr,"Call failed\n"); return NULL ; } } else { if (PyErr_Occurred()) PyErr_Print(); fprintf(stderr, "Cannot find 'unpickle' function\n") ; } Py_XDECREF(pFunc); Py_DECREF(pModule); } else { PyErr_Print(); fprintf(stderr, "Failed to load python script file\n"); } Py_Finalize() ; return unpickledString ; }

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Unicode compatibility
by Daniel Stutzbach 26 May '10

26 May '10

I'm working on http://bugs.python.org/issue8654 and I'd like to get some feedback from extension-writers, since it will impact them. Synopsis of the problem: If you try to load an extension module that: - uses any of Python's Unicode functions, and - was compiled by a Python with the opposite Unicode setting (UCS2 vs UCS4) then you get an ugly "undefined symbol" error from the linker. For Python 3, __repr__ must return a Unicode object which means that almost all extensions will need to call some Unicode functions. It's basically fruitless to upload a binary egg for Python 3 to PyPi, since it will generate link errors for a large fraction of downloaders (as I discovered the hard way). Proposed solution: By default, extensions will compile in a "Unicode-agnostic" mode, where Py_UNICODE is an incomplete type. The extension's code can pass Py_UNICODE pointers back and forth between Python API functions, but it cannot dereference them nor use sizeof(Py_UNICODE). Unicode-agnostic modules will load and run in both UCS2 and UCS4 interpreters. Most extensions fall into this category. If a module needs to dereference Py_UNICODE, it can define PY_REAL_PY_UNICODE before including Python.h to make Py_UNICODE a complete type, .Attempting to load such a module into a mismatched interpreter will cause an ImportError (instead of an ugly linker error). If an extension uses PY_REAL_PY_UNICODE in any .c file, it must also use it in the .c file that calls PyModule_Create to ensure the Unicode width is stored in the module's information. I have two questions for the greater community: 1) Do you have any fundamental concerns with this design? 2) Would you prefer the default be reversed? i.e, that Py_UNICODE be a complete type by default, and an extension must have a #define to compile in Unicode-agnostic mode? -- Daniel Stutzbach, Ph.D. President, Stutzbach Enterprises, LLC <http://stutzbachenterprises.com>

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New Here
by Emeka 25 May '10

25 May '10

Hello All, Is there any tutorial I can read beside manual? Regards, Emeka

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Some type inference for python?
by Issyk Kol 25 May '10

25 May '10

Hello. I'd like to do some ML-like type inference for Python code. I'm not trying to resurrect the static typing vs. dynamic typing debate here. It's simply that I'd need to get static typing for Python for code-generation reasons. Therefore, I'd like to ask: Does the Python C API support a way to inspect the bytecode or the source code of a given piece of Python code? What approach would be promising enough to type things in ML-way (I'm unfortunately not interested in cartesian-product type inference), and what help may the C API provide to meet this goal? (Maybe I haven't looked far enough, but I could not discern clearly what could be useful...) (Sorry for posting in non-text-mode. Using a webmail because port 25 policies in this bloody country ar sooooo restrictive.) Thanks. Issyk Kol.

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Checking int type
by Vojtěch Rylko 24 May '10

24 May '10

Hi, what am I doing wrong? C code: -------------- static PyObject *is_prime(PyObject *self, PyObject *value) { if (!PyInt_Check(value)) { PyErr_SetString(PyExc_TypeError, "only integers are acceptable"); return NULL; } -------------- Test (I'm using integer 3): ------------ >>> primes.is_prime(3) Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: only integers are acceptable ------------- Thanks

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