PyArray_FromDims segfault??
Hello, I would like to use PyObject_CallObject to call the imshow function from matplolib from a C code. So, the first step is to create a 2D PyArrayObject from a C array. I have read the Numpy book which is great but now I'm puzzled: My goal is to convert a C array of doubles into a 2D numpy array object. PyArray_SimpleNewFromData(nd, dims, typenum, data) seems to be the function I need but I did not manage to write/find any compiling *and* not segfaulting code performing this convertion :( Ok, maybe PyArray_SimpleNewFromData is to complex to begin with. Let's try with PyArray_FromDims... segfault also :( My code looks so simpleKK I cannot see what I'm doing the wrong way :( #include <python2.4/Python.h> #include <numpy/arrayobject.h> int main (int argc, char *argv[]) { PyArrayObject *array; int i, length = 100; double* a; double x; Py_Initialize (); array = (PyArrayObject *) PyArray_FromDims(1, &length, PyArray_DOUBLE); a = new double[100]; for (i = 0; i < length; i++) { x = (double) i/(length-1); a[i] = x; } Py_Finalize (); return 0; } g++ imshow.cpp -o imshow -lpython2.4 -I/usr/lib/python2.4/site-packages/numpy/core/include/ ./imshow -> Segmentation fault I really need the Py_Initialize/Py_Finalize calls because it is 'embedding python' (and not extending :)). To sum up, any code taking an double* and 2 int standind for the dimX and the dimY and returning the corresponding PyObject would be very much appreciated :) I don't care if it has to copy the data. The simpler the better. In [2]: numpy.__version__ Out[2]: '1.0.2.dev3491' Xavier. ps : I really want to use only the C API first at all to learn it and because it really looks like as the simple way to fit my needs. Ok PyObject_CallObject needs quite a lot of additionnal code but it is always almost the same :) -- ############################################ Xavier Gnata CRAL - Observatoire de Lyon 9, avenue Charles André 69561 Saint Genis Laval cedex Phone: +33 4 78 86 85 28 Fax: +33 4 78 86 83 86 E-mail: gnata@obs.univ-lyon1.fr ############################################
Xavier Gnata wrote:
Hello,
I would like to use PyObject_CallObject to call the imshow function from matplolib from a C code. So, the first step is to create a 2D PyArrayObject from a C array.
I have read the Numpy book which is great but now I'm puzzled: My goal is to convert a C array of doubles into a 2D numpy array object. PyArray_SimpleNewFromData(nd, dims, typenum, data) seems to be the function I need but I did not manage to write/find any compiling *and* not segfaulting code performing this convertion :(
Ok, maybe PyArray_SimpleNewFromData is to complex to begin with. Let's try with PyArray_FromDims... segfault also :(
My code looks so simpleKK I cannot see what I'm doing the wrong way :(
#include <python2.4/Python.h> #include <numpy/arrayobject.h>
int main (int argc, char *argv[]) {
PyArrayObject *array; int i, length = 100; double* a; double x; Py_Initialize ();
array = (PyArrayObject *) PyArray_FromDims(1, &length, PyArray_DOUBLE);
a = new double[100]; for (i = 0; i < length; i++) { x = (double) i/(length-1); a[i] = x; } Py_Finalize ();
return 0; }
g++ imshow.cpp -o imshow -lpython2.4 -I/usr/lib/python2.4/site-packages/numpy/core/include/
./imshow -> Segmentation fault
I really need the Py_Initialize/Py_Finalize calls because it is 'embedding python' (and not extending :)).
To sum up, any code taking an double* and 2 int standind for the dimX and the dimY and returning the corresponding PyObject would be very much appreciated :) I don't care if it has to copy the data. The simpler the better.
You *always* need to use import_array() or one of it's variants somewhere in your code. In this case, because you are returning from main, you need to use: import_array1(-1) in order to return -1 on import error. The import array sets up the C-API so it can be used. Also, this code is not doing anything with the memory you just created for array. If you want to use pre-existing memory, then PyArray_SimpleNewFromData will work and construct a PyObject * (an ndarray object) where the memory is the pointer you pass in for the data-area to that function. You must be sure that the memory is not released before the returned object is used up or you will get segmentation faults. -Travis
participants (2)
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Travis Oliphant -
Xavier Gnata