Creating exception class with custom fields in Python/C API

[ty ty]

Hello, list!

I'm writing a wrapper for C-library. When something goes wrong in that library, i can get error details. And i want to assign them to fields of my own exception class.

For this purpose, i looked throught Modules/_ctypes/_ctypes.c (in python source tree) and implemented same things. Briefly:

 define PyObject * Error in header file, 
 write init and other necessary functions 
 assign them to PyMethodDef array
 initialize class's dict with methods above (in function create_error)
 create new exception with no base class and with dict (in function create_error)
 call to create_error and assign Error class to module (PyModule_AddObject)
 throw error with PyErr_SetObject(Error, tpl);, where tpl is tuple with error details, which are assigned to Error's fields in init function
All of this is consistent with what i saw in Modules/_ctypes/_ctypes.c, i think. But it doesn't work: when i call PyErr_SetObject(Error, tpl);, Python's runtime raises error:
TypeError: unbound method __init__() must be called with Error instance as first argument (got str instance instead)

And PyObject_Print(Error, stdout, 0); returns:
{'__init__': <unbound method Error.__init__> ...}

It's item for init function in PyMethodDef array:
{"__init__", myerror_init, METH_VARARGS, "initialize error"}

and it's function's signature:
static PyObject * myerror_init(PyObject * self, PyObject *args)

(python version -- 2.6.4)

Why methods are unbound? And what i've missed? Or what is the right and pythonic way to define exception with custom class attributes?

Thanks.

(crosspost from stackoverflow: http://stackoverflow.com/questions/3118617/creating-exception-class-with-custom-fields-in-python-c-api )