Embeding Py: failed to instantiate a class

Brano Zarnovican zarnovican at pobox.sk
Wed Mar 23 08:40:32 CET 2005


Hi !

I need to import a module and create an instance
of a class from that module (in C).

import mod
o = mod.klass()

(mod.klass is a subclass of tuple)

When I receive a class object from the module..

module = PyImport_ImportModule("mod")
cls = PyObject_GetAttrString(module, "klass")

..it fails the PyClass_Check(cls) check.

Some classes pass the check, like:
class test1:
  pass
class test3(test1):
  pass

but most don't. It is enough to subclass
a buildin type. E.g. this class fails the check:
class test2(object):
  pass

Q: Do I need to initialize the class object in
  some way ? How ?

Thanks,

BranoZ

PS: Below are some example code used to test it.

--- mod.py ---
class test1:
  pass

class test2(object):
  pass

class test3(test1):
  pass

--- main.c ---
#include <Python.h>

static PyObject *module = NULL;

void check(char *name) {
    PyObject *cls = NULL;

    printf("%s - ", name);
    if ((cls=PyObject_GetAttrString(module, name)) == NULL) {
        PyErr_Print();
        return;
    }
    PyObject_Print(cls, stdout, 0);
    if (!PyClass_Check(cls))
        printf(" - not a class!!\n");
    else
        printf(" - is a class.\n");
}

int main(int argc, char *argv[]) {

    Py_Initialize();

    if ((module=PyImport_ImportModule("mod")) == NULL) {
        PyErr_Print();
        return -1;
    }
    check("test1");
    check("test2");
    check("test3");

    Py_Main(argc, argv);
    Py_Finalize();
}

--- output ---
$ ./main
test1 - <class mod.test1 at 0x4032da7c> - is a class.
test2 - <class 'mod.test2'> - not a class!!
test3 - <class mod.test3 at 0x4032db3c> - is a class.
Python 2.3 (#2, Feb  9 2005, 13:41:20)
[GCC 3.3.1 (Mandrake Linux 9.2 3.3.1-2mdk)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import mod
>>> mod.test1
<class mod.test1 at 0x4032da7c>
>>> mod.test2
<class 'mod.test2'>
>>> mod.test1()
<mod.test1 instance at 0x40337cac>
>>> mod.test2()
<mod.test2 object at 0x40337cec>
>>>




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