[C++-sig] create boost array from a Numpy PyArray without copying data?

[Sebastian Walter]

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Hello,
On the C++ side I have a raw pointer: double *x;
I'd like to change its values from within Python by using Numpy.
Example code can be found below.

My approach is
1) make PyArray from existing data *x with PyArray_SimpleNewFromData
2) create a boost array from the PyArray.

My question is:
How can I create a
boost::python::numeric::array from a Numpy Pyarray without copying data?


Here my best shot... (compiles and runs but copies the data)
- ----------------- test.cpp ------------------

#define PY_ARRAY_UNIQUE_SYMBOL PyArrayHandle
#include <iostream>
#include <boost/python.hpp>
#include <numpy/noprefix.h>

using namespace std;
using namespace boost;
using namespace boost::python;
using namespace boost::python::numeric;

array test_function(){
	int N = 3;
	double x[] = {1.,2.,3.};
	array numpy_x(static_cast<array>(handle<>(PyArray_SimpleNewFromData(1,
&N, PyArray_DOUBLE, x))));
	double *y = static_cast<double*> PyArray_DATA(numpy_x.ptr());
	y[0] = 37.;

	for(int n = 0; n<N; ++n){
		cout<<"numpy_x[n]="<<y[n]<<"\t\t"<<"x[n]="<<x[n]<<endl;
	}
	return numpy_x;
}


BOOST_PYTHON_MODULE(_test)
{
	import_array();
	array::set_module_and_type("numpy", "ndarray");
	def("test_function", test_function);
}


- ----------- test.py -----------------
from _test import *

if __name__ == "__main__":
	print test_function()

- --------------- shell output --------------------
$python test.py
numpy_x[n]=37           x[n]=1
numpy_x[n]=2            x[n]=2
numpy_x[n]=3            x[n]=3
[ 37.   2.   3.]



It would be great if anyone knew the answer to my problem.

regards,
Sebastian Walter
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