python - Use struct in SWIG argout typemap -

i want call c function python, should create , initialize struct. want struct converted python object return value in python.

here example files (based on accessing c struct array python swig) achieve want, i.e. create_struct() creates , initializes struct, can used in python. john bollinger helping fix bugs.

example.h

#include <stdint.h>  struct foo {   uint8_t a[4]; };  void create_struct(struct foo** new_struct); 

example.c

#include <string.h> #include "example.h"  void create_struct(struct foo** new_struct){     struct foo* foo = (struct foo*) malloc(sizeof(struct foo));     uint8_t tmp[4] = {0,1,2,3};     memcpy(foo->a, tmp, 4);     *new_struct = foo; } 

example.i

%module example %{ #define swig_file_with_init #include "example.h" %}  // define input , output typemaps  %typemap(in) uint8_t a[4] {   if (!pybytes_check($input)) {     pyerr_setstring(pyexc_typeerror, "expecting bytes parameter");     swig_fail;   }    if (pyobject_length($input) != 4) {     pyerr_setstring(pyexc_valueerror, "expecting bytes parameter 4 elements");     swig_fail;   }    uint8_t res[4];   char* bytes = pybytes_asstring($input);   int i;   (i=0; i<4; i++) {     res[i] = (uint8_t) bytes[i];   }    $1 = res; }  %typemap(out) uint8_t a[4] {     $result = pybytes_fromstringandsize((char*) $1, 4); }  /*  * fails "warning 453: can't apply (struct foo *output). no typemaps defined.":  *   %apply struct foo* output {struct  foo* new_struct };  * i'm trying define typemaps struct foo*  */  // typemap suppresses requiring parameter input. %typemap(in,numinputs=0) struct foo** new_struct (struct foo* temp) {   $1 = &temp; }  %typemap(argout) struct foo** new_struct {     $result = swig_newpointerobj(*$1, $descriptor(struct foo*), swig_pointer_own); }  %include "example.h"  extern void create_struct(struct foo** new_struct); 

setup.py

#!/usr/bin/env python3  distutils.core import setup, extension  module1 = extension('example', sources=['example.c', 'example.i']) setup(name='example', version='0.1', ext_modules=[module1]) 

test.py

#!/usr/bin/env python3  import example foo = example.create_struct() print("foo.a: %r" % foo.a) 

build , execute:

python3 setup.py build_ext --inplace && mv example.*.so _example.so && python3 test.py 

the test code should print foo.a: b'\x00\x01\x02\x03'.