Extension types as exceptions (Wrapup)

[Michael P. Reilly]

Daniel Dittmar <daniel.dittmar at sap-ag.de> wrote:
: Thanks for the help,

: for those with similar problems, code to create the exception type
: follows:

: static PyObject *
: createExceptionKind (
:     const char * exceptionName,
:     const char * exceptionCode)
: {
:     PyObject * result;
:     PyObject * runResult = NULL;
:     PyObject * globals = NULL;
:     PyObject * locals = NULL;

:     if (exceptionCode != NULL) {
:         globals = PyDict_New ();
:         locals = PyDict_New ();
:         runResult = PyRun_String ((char *) exceptionCode,\
: Py_file_input,
:             globals, locals);
:     }
:     result = PyErr_NewException ((char *) exceptionName, \
: NULL,locals);
:     Py_XDECREF (locals);
:     Py_XDECREF (globals);
:     Py_XDECREF (runResult);
:     return result;
: }

: Parameter exceptionName is something of the form "mymod.ExceptionName"
: Parameter exceptionCode is something like
: "def __str__ (self):\n    return 'ExceptionName: %d %s' % (self.code,
: self.msg\n"

: Error handling is a bit weak as I call this from module
: initialization, which does it's own checking

: Code to create a new exception:

: static void
: raiseError (
:     int code,
:     const char * msg)
: {
:     PyObject * exception = PyInstance_New (ErrorType, NULL, NULL);

:     if (exception == NULL) {
:         return;
:     }
:     PyObject_SetAttrString(exception,"code", PyInt_FromLong  (code));
:     PyObject_SetAttrString(exception,"msg", PyString_FromString(msg));
:     PyErr_SetObject (ErrorType, exception);
: }

: ErrorType is a c module static which contains the result of
: createExceptionKind

You could probably also do:

  PyObject *exc_args;
  exc_args = Py_BuildValue("is", code, msg);
  PyErr_SetObject(ErrorType, exc_args);

If the data isn't an exception instance, it creates one with the data
given.

As a good tip, return (PyObject *)NULL in your function, this lets you
use in your code:
  return raiseError(27, "I don't know what happened");

instead of:
  { raiseError(27, "I don't know what happened");
    return NULL;
  }

  -Arcege