％exception被SWIG（python）包装器忽略了吗？

Question

I am trying to wrap a C lib to python mod with SWIG, but I am having trouble getting exceptions to work. Here is a little example of the code,

except_test.i

%module except_test
%{
#include "except_test.h"
#include <stdio.h>
%}

%include "except_test.h"

%{
static int flagged_exception = 0;

void throw_except()
{
    flagged_exception = 1;
}
%}

%exception {
    $action
    if (flagged_exception) {
        PyErr_SetString(PyExc_RuntimeError, "test except");
        flagged_exception = 0;
    }
}

except_test.c:

int except_test(int a) {

    if (a < 0) {
        throw_except();
        return 0;
    } else{
        return -1;
    }
}

Then when I ran the except_test() function, exception is not thrown

run_except.py

from except_test import *

b = except_test(-1)
print 'b=', b

run:

$ python run_except.py 
b= 0
$

What is wrong here?

Answer 1

Declare the %exception before processing the except_test.h header; otherwise, it won't be active when the function is wrapped in SWIG:

%module except_test
%{
#include "except_test.h"
#include <stdio.h>
%}

%exception {
    $action
    if (flagged_exception) {
        PyErr_SetString(PyExc_RuntimeError, "test except");
        flagged_exception = 0;
        return NULL; // ** need to add this **
    }
}

%include "except_test.h"

%{
static int flagged_exception = 0;

void throw_except()
{
    flagged_exception = 1;
}
%}

Result:

>>> import except_test
>>> except_test.except_test(-1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: test except