Python C Extension

Following Andrew Dalke's example, this is perhaps the simplest possible C extension for Python. For explanation of what's happening, see his page.

[ Something's gone wacko with this post---it's single spaced in preview, double after posting ]

x.c

#include <math.h> #include "Python.h" int process (const char *c, double f) { int i = 0; if (c[0] == 'c') { i = floor(f); } return i; } PyDoc_STRVAR(x__doc__, "x module for process'ing stuff"); PyDoc_STRVAR(process__doc__, "c,f -> do something with f if c == 'c'"); static PyObject * py_process(PyObject *self, PyObject *args) { double f = 0; char *c; int i; if (!PyArg_ParseTuple(args, "sd:process", &c, &f)) return NULL; i = process(c,f); return PyInt_FromLong((long) i); } static PyMethodDef x_methods[] = { {"process", py_process, METH_VARARGS, process__doc__}, {NULL, NULL} /* sentinel */ }; PyMODINIT_FUNC initx(void) { Py_InitModule3("x", x_methods, x__doc__); }

setup.py

from distutils.core import setup, Extension setup(name="x", version="0.0", ext_modules = [Extension("x", ["x.c"])])

> python setup.py build running build running build_ext building 'x' extension creating build creating build/temp.macosx-10.6-universal-2.6 gcc-4.2 -fno-strict-aliasing -fno-common -dynamic -DNDEBUG -g -fwrapv -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch ppc -arch x86_64 -pipe -I/System/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6 -c x.c -o build/temp.macosx-10.6-universal-2.6/x.o creating build/lib.macosx-10.6-universal-2.6 gcc-4.2 -Wl,-F. -bundle -undefined dynamic_lookup -arch i386 -arch ppc -arch x86_64 build/temp.macosx-10.6-universal-2.6/x.o -o build/lib.macosx-10.6-universal-2.6/x.so

You can control which architecture is build via setup.py with:

export ARCHFLAGS="-arch x86_64"

> ln -s build/lib.macosx-10.6-universal-2.6/x.so x.so > > python -c "import math; import x; print x.process('c',math.pi)" 3 > python -c "import math; import x; print x.process('a',math.pi)" 0 > python Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import x >>> x.__doc__ "x module for process'ing stuff" >>> x.process.__doc__ "c,f -> do something with f if c == 'c'" >>>

Looks good.

Note: on my 64-bit machines I'm getting a warning:

x.c: In function ‘process’: x.c:7: warning: implicit conversion shortens 64-bit value into a 32-bit value

Converting i to long doesn't help. I'll try to look into that.