Passing Python array to c++ function with SWIG

Question

I have written a good bit of code in python and it works great. But now I\'m scaling up the size of the problems that I\'m analyzing and python is dreadfully slow. The slow

Answer 1

You can use arrays as it is described here: Doc - 5.4.5 Arrays, the carray.i or std_vector.i from the SWIG library. I find it easier to work with std::vector from the SWIG library std_vector.i to send a python list to a C++ SWIG extension. Though in your case where optimization matters, it may not be the optimal.

In your case you can define:

test.i

%module test
%{
#include "test.h"
%}

%include "std_vector.i"

namespace std {
%template(Line)  vector < int >;
    %template(Array) vector < vector < int> >;
}   

void print_array(std::vector< std::vector < int > > myarray);

test.h

#ifndef TEST_H__
#define TEST_H__

#include <stdio.h>
#include <vector>

void print_array(std::vector< std::vector < int > > myarray);

#endif /* TEST_H__ */

test.cpp

#include "test.h"

void print_array(std::vector< std::vector < int > > myarray)
{
    for (int i=0; i<2; i++)
        for (int j=0; j<2; j++)
            printf("[%d][%d] = [%d]\n", i, j, myarray[i][j]);
}

If you run the following python code (I used python 2.6.5), you can see that the C++ function can access the python list:

>>> import test
>>> a = test.Array()
>>> a = [[0, 1], [2, 3]]
>>> test.print_array(a)
[0][0] = [0]
[0][1] = [1]
[1][0] = [2]
[1][1] = [3]