Python bindings for a vala library

Question

I am trying to create python bindings to a vala library using the following IBM tutorial as a reference.

My initial directory has the following two files:

test.vala

using GLib;

namespace Test {

   public class Test : Object {
       public int sum(int x, int y) {
           return x + y;
       }
   }

}

test.override

%%
headers
#include <Python.h> 
#include "pygobject.h"
#include "test.h"
%%
modulename test
%%
import gobject.GObject as PyGObject_Type
%%
ignore-glob
  *_get_type
%%

and try to build the python module source test_wrap.c using the following code

build.sh

#/usr/bin/env bash

valac test.vala -CH test.h
python /usr/share/pygobject/2.0/codegen/h2def.py test.h > test.defs
pygobject-codegen-2.0 -o test.override -p test test.defs > test_wrap.c

However, the last command fails with an error

$ ./build.sh 
Traceback (most recent call last):
  File "/usr/share/pygobject/2.0/codegen/codegen.py", line 1720, in <module>
    sys.exit(main(sys.argv))
  File "/usr/share/pygobject/2.0/codegen/codegen.py", line 1672, in main
    o = override.Overrides(arg)
  File "/usr/share/pygobject/2.0/codegen/override.py", line 52, in __init__
    self.handle_file(filename)
  File "/usr/share/pygobject/2.0/codegen/override.py", line 84, in handle_file
    self.__parse_override(buf, startline, filename)
  File "/usr/share/pygobject/2.0/codegen/override.py", line 96, in __parse_override
    command = words[0]
IndexError: list index out of range

Is this a bug in pygobject, or is something wrong with my setup? What is the best way to call code written in vala from python?

EDIT: Removing the extra line fixed the current problem, but now as I proceed to build the python module, I am facing another problem. Adding the following C file to the existing two in the directory:

test_module.c

#include <Python.h>

void test_register_classes (PyObject *d);
extern PyMethodDef test_functions[];

DL_EXPORT(void)
inittest(void)
{
  PyObject *m, *d;
  init_pygobject();
  m = Py_InitModule("test", test_functions);
  d = PyModule_GetDict(m);
  test_register_classes(d);
  if (PyErr_Occurred ()) {
      Py_FatalError ("can't initialise module test");
  }
}

and building with the following script

build.sh

#/usr/bin/env bash

valac test.vala -CH test.h
python /usr/share/pygobject/2.0/codegen/h2def.py test.h > test.defs
pygobject-codegen-2.0 -o test.override -p test test.defs > test_wrap.c

CFLAGS="`pkg-config --cflags pygobject-2.0` -I/usr/include/python2.6/ -I."
LDFLAGS="`pkg-config --libs pygobject-2.0`"

gcc $CFLAGS -fPIC -c test.c 
gcc $CFLAGS -fPIC -c test_wrap.c 
gcc $CFLAGS -fPIC -c test_module.c
gcc $LDFLAGS -shared test.o test_wrap.o test_module.o -o test.so

python -c 'import test; exit()'

results in an error:

$ ./build.sh 
***INFO*** The coverage of global functions is 100.00% (1/1)
***INFO*** The coverage of methods is 100.00% (1/1)
***INFO*** There are no declared virtual proxies.
***INFO*** There are no declared virtual accessors.
***INFO*** There are no declared interface proxies.
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: ./test.so: undefined symbol: init_pygobject

Where is the init_pygobject symbol defined? What have I missed linking to?

Answer 1

You can go with GObject Introspection.

This repository contains samples how to auto-bind vala libraries to other languages:

https://github.com/antono/vala-object