Passing structure between Python and C using SWIG

Question

I'm trying to pass a structure between C and Python using SWIG. I am completely new to Python and C. I searched for passing structure using SWIG , without success.

I based my code on examples from SWIG Python tutorial , page 55 and 56. It should fetch the input values from Python, multiply them by 2 in C and return the results to Python. I am getting the error AttributeError: 'module' object has no attribute 'new_info .

sample.c

#include <stdio.h>
#include "sample.h"

struct info sample;

void getstruct (struct info *sample);

void getstruct (struct info *sample) {

   int i = 0;
   int j = 0;
   int k = 0;
   int l = 0;

   i = 2 * sample->i;
   j = 2 * sample->j;
   k = 2 * sample->k;
   l = 2 * sample->l;

   sample->i = i;
   sample->j = j;
   sample->k = k;
   sample->l = l;

   return(&sample);

}

sample.i

%module sample
%{
typedef struct
{
   int i;
   int j;
   int k;
   int l;
} info;

extern void getstruct (struct info *sample);

info *new_info(int i, int j, int k, int l) {
    info *in = (info *) malloc(sizeof(info));
    in->i = i;
    in->j = j;
    in->k = k;
    in->l = l;
    return in;
}

void delete_info(info *in) {
    free(in);
}
%}

extern void getstruct (struct info *sample);
typedef struct
{
   int i;
   int j;
   int k;
   int l;
} info;

Command executed to build the wrapper:

swig -python sample.i
gcc -fPIC -c sample.c sample_wrap.c -I/usr/include/python2.7
ld -shared sample.o sample_wrap.o -o _sample.so

Python error:

[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sample
>>>
>>> print sample
<module 'sample' from 'sample.pyc'>
>>> print sample.getstruct(1,2,3,4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: getstruct() takes exactly 1 argument (4 given)
>>> v = new_info(1,2,3,4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'new_info' is not defined
>>> v = sample.new_info(1,2,3,4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'new_info'
>>>

Answer 1

In the sample.i file, you've added the new_info and delete_info functions to the wrapper code directly by declaring it within %{ and %} , but did not tell SWIG to generate wrappers for those functions. Either repeat the code again outside the %{ / %} , or use %inline %{ / %} . The latter adds the code directly to the wrapper as well as tells SWIG to wrap it.