On Mon, Dec 22, 2008 at 10:06 AM, <chojra...@gmail.com> wrote:
> On Mon, Dec 22, 2008 at 03:29, Guilherme Polo <ggp...@gmail.com> wrote:
>> On Sun, Dec 21, 2008 at 11:02 PM, <chojra...@gmail.com> wrote:
>>> Hello,
>>>
>>> I'm trying to implement custom exception that have to carry some
>>> useful info by means of instance members, to be used like:
>>>
>>> try:
>>> // some code
>>> except MyException, data:
>>> // use data.errorcode, data.errorcategory, data.errorlevel,
>>> data.errormessage and some others
>>>
>>> The question is - how to implement the instance variables with
>>> PyErr_NewException?
>>
>> Using PyErr_NewException is fine. You must understand that an
>> exception is a class, and thus PyErr_NewException creates one for you
>> and returns it.
>> Just like you would do with a class that has __dict__, set some
>> attributes to what you want. That is, use PyObject_SetAttrString or
>> something more appropriated for you.
>
> Ok so I did the following. In init function (forget refcounting and
> error checking for a moment ;-)
>
> PyObject *dict = PyDict_New();
> PyDict_SetItemString(dict, "errorcode", PyInt_FromLong(0));
> static PyObject *myexception =
> PyErr_NewException("module.MyException", NULL, dict);
You do not really have to create a dict here, one will be created for
you if you pass a NULL there.
> PyModule_AddObject(module, "MyException", myexception);
>
> It worked more or less as expected, the help shown:
>
> | ----------------------------------------------------------------------
> | Data and other attributes defined here:
> |
> | errorcode = 0
> |
> | ----------------------------------------------------------------------
>
> Then I did the following when raising the exception:
>
> PyObject_SetAttrString(myexception, "errorcode", PyInt_FromLong(111));
> PyErr_SetString(myexception, "Bad thing happened");
> return NULL;
>
> and the test code was:
> try:
> do_bad_thing();
> except MyException, data:
>
> and you surely already guessed it -- data.errorcode was 0.... Not only
> that, module.MyException.errorcode was also 0...
>
> What I'm doing wrong? I certainly don't get the idea of exceptions in
> Python, especially what is being raised - a class or an instance?
There are two forms raise can take, both will end up involving a class
and a intsance.
> If
> the latter - how's the class instantiated?
You can call a class to instantiate it.
> If not - what about values
> in different threads? The docs are so vague about that...
>
>
> Thanks again in advance,
> Chojrak
>
Again, an exception is a class, so you could create a new type in C,
and do anything you wanted. But you probably don't want to create a
new type to achieve this, so there are two simple ways I'm going to
paste below:
#include "Python.h"
static PyObject *MyErr;
static PyMethodDef module_methods[] = {
{"raise_test", (PyCFunction)raise_test, METH_NOARGS, NULL},
{NULL},
};
PyMODINIT_FUNC
initfancy_exc(void)
{
PyObject *m;
m = Py_InitModule("fancy_exc", module_methods);
if (m == NULL)
return;
MyErr = PyErr_NewException("fancy_exc.err", NULL, NULL);
Py_INCREF(MyErr);
if (PyModule_AddObject(m, "err", MyErr) < 0)
return;
}
the raise_test function is missing, pick one of these:
static PyObject *
raise_test(PyObject *self)
{
PyObject_SetAttrString(MyErr, "code", PyInt_FromLong(42));
PyObject_SetAttrString(MyErr, "category", PyString_FromString("nice
one"));
PyErr_SetString(MyErr, "All is good, I hope");
return NULL;
}
or
static PyObject *
raise_test(PyObject *self)
{
PyObject *t = PyTuple_New(3);
PyTuple_SetItem(t, 0, PyString_FromString("error message"));
PyTuple_SetItem(t, 1, PyInt_FromLong(10));
PyTuple_SetItem(t, 2, PyString_FromString("category name here"));
PyErr_SetObject(MyErr, t);
Py_DECREF(t);
return NULL;
}
In this second form you check for the args attribute of the exception.
--
-- Guilherme H. Polo Goncalves
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