Dear Henry, You need to call import_array() in initspam. See: http://docs.scipy.org/doc/numpy-1.5.x/user/c-info.how-to-extend.html HTH, Jon On 29/10/2010 15:11, Henry Gomersall wrote:
I'm trying to get a really simple toy example for a numpy extension working (you may notice its based on the example in the numpy docs and the python extension docs). The code is given below.
The problem I am having is running the module segfaults at any attempt to access&PyArray_Type (so, as presented, the segfault occurs at the call to PyArg_ParseTuple). I've been assuming that importing numpy into the calling python code implicitly provides the numpy libraries that are necessary for linking. I can only assume I'm missing something. Do i need some additional includes etc in my compile flags?
I'm currently using the distutils.core module and not the distutils module that comes with numpy if that makes a difference.
I'm actually pretty keen to document what I've learnt as a 5 minute how-to for writing basic numpy extensions, if there is demand for it. It doesn't seem to exist as a coherent whole at the moment.
Thanks,
Henry
#include<Python.h> #include<numpy/arrayobject.h>
PyMODINIT_FUNC initspam(void);
static PyObject * spam_system(PyObject *self, PyObject *args);
void worker_function(double *input, double *output, npy_intp size);
static PyMethodDef SpamMethods[] = { {"system", spam_system, METH_VARARGS, "Execute a shell command."}, {NULL, NULL, 0, NULL} /* Sentinel */ };
PyMODINIT_FUNC initspam(void) { (void) Py_InitModule("spam", SpamMethods); }
static PyObject * spam_system(PyObject *self, PyObject *args) { int n; int ndims;
PyObject *inarg=NULL, *outarg=NULL; PyObject *inarr=NULL, *outarr=NULL;
/* Both input and output need to be PyArray_Type type*/ if (!PyArg_ParseTuple(args, "O!O!",&PyArray_Type,&inarg, &PyArray_Type,&outarg)); return NULL;
inarr = PyArray_FROM_OTF(inarg, NPY_DOUBLE, NPY_IN_ARRAY); if (inarr == NULL) goto fail;
outarr = PyArray_FROM_OTF(outarg, NPY_DOUBLE, NPY_OUT_ARRAY); if (outarr == NULL) goto fail;
/* Check the shape of the two arrays is the same */ ndims = ((PyArrayObject *)outarr)->nd; if (((PyArrayObject *)inarr)->nd != ndims) goto fail;
/* ...still checking...*/ for (n=1; n<ndims; n++) { if (PyArray_DIM(inarr,n) != PyArray_DIM(outarr,n)) goto fail; }
/* Now actually do something with the arrays */ worker_function((double *)PyArray_DATA(inarr), (double *)PyArray_DATA(outarr), PyArray_Size(inarr));
Py_DECREF(inarr); Py_DECREF(outarr); return Py_None;
fail: Py_XDECREF(inarr); Py_XDECREF(outarr); return NULL; }
void worker_function(double *input, double *output, npy_intp size) { npy_intp n;
for (n=0;n<size;n++) { output[n] = input[n] + 10; } return; }
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