On Fri, Oct 30, 2015 at 11:15 PM, laurentes <laurentelshafey@gmail.com> wrote:

Using Swig, I don't manage to (properly) create the Python Binding for the following C-like function:

void add_array(double* input_array1, double* input_array2, double* output_array, int length);

where the three arrays have all the same length.

do you have to use SWIG? this would be really easy in Cython.... cdef cdef extern from "your_header.h": void add_array(double* input_array1, double* input_array2, double* output_array, int length) def py_add_array( np.ndarray[double, ndim=1] arr1, np.ndarray[double, ndim=1] arr2): cdef int length if arr1.shape != arr2.shape: raise ValueError("Arrays must be the same size") length = arr1.shape[0] cdef np.ndarray[double, ndim=1] out_arr = np.empty((length), dtype=np.float64) add_array(&arr1[0], &arr2[0], &out_arr[0], length) return out_arr Untested and from memory -- but you get the idea. -CHB

...

This is similar to this thread <

http://numpy-discussion.10968.n7.nabble.com/Numpy-SWIG-td25709.html#a25710

...

, which has never been fully addressed online.

From Python, I would like to be able to call:

add_array(input_array1, input_array2)

which would return me a newly allocated NumPy array (output_array) with the result.

In my Swig file, I've first used the wrapper function trick described here < http://web.mit.edu/6.863/spring2011/packages/numpy_src/doc/swig/doc/numpy_sw...

...

, that is:

%apply (double* IN_ARRAY1, int DIM1) {(double* input_array1, int length1), (double* input_array2, int length2)}; %apply (double* ARGOUT_ARRAY1, int DIM1) {(double* output_array, int length3)};

%rename (add_array) my_add_array; %exception my_add_array { $action if (PyErr_Occurred()) SWIG_fail; } %inline %{ void my_add_array(double* input_array1, int length1, double* input_array2, int length2, double* output_array, int length3) { if (length1 != length2 || length1 != length3) { PyErr_Format(PyExc_ValueError, "Arrays of lengths (%d,%d,%d) given", length1, length2, length3); } else { add_array(input_array1, input_array2, output_array, length1); } } %}

This allows me to call the function from Python using add_array(input_array1, input_array2, length). But the third argument of this function is useless and this function does not look 'Pythonic'.

Could someone help me to modify my Swig file, such that only the first two arguments are required for the Python API?

Thanks a lot, Laurent

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