C++ Exceptions in SWIG typemaps - c++

Question

I'm trying to use C++ to wrap some simple C++ and encountered an issue when trying to wrap even the most basic stuff.
SWIG doesn't seem to try and catch and exception that might occurr inside a typemap.
For example for the following SIWG interface file:
%module badswig
std::string func();
SWIG Generates this:
SWIGINTERN PyObject *_wrap_func(PyObject *SWIGUNUSEDPARM(self), PyObject *args) {
PyObject *resultobj = 0;
std::string result;
if (!PyArg_ParseTuple(args,(char *)":func")) SWIG_fail;
result = func();
resultobj = SWIG_NewPointerObj((new std::string(static_cast< const std::string& >(result))), SWIGTYPE_p_std__string, SWIG_POINTER_OWN | 0 );
return resultobj;
fail:
return NULL;
}
Notice that new std::string is unprotected at all so that if std::bad_alloc will be thrown it will propogate to Python and crash.
There are likely other cases as well not only SWIG using new.
There is %exception which handles this for the wrapped function (If func() throws) but I couldn't find anything to handle this for typemaps, especially for ones supplied by SWIG.
Am I missing something? is there someway to correctly handle this?
EDIT:
In response to an answer and to clarify my question, %exception does not achive what I want:
%module badswig
%exception %{
try {
$action
} catch (const std::bad_alloc&) {
PyErr_NoMemory();
SWIG_fail;
}
%}
std::string func();
Generates this:
SWIGINTERN PyObject *_wrap_func(PyObject *SWIGUNUSEDPARM(self), PyObject *args) {
PyObject *resultobj = 0;
std::string result;
if (!PyArg_ParseTuple(args,(char *)":func")) SWIG_fail;
try {
result = func();
} catch (const std::bad_alloc&) {
PyErr_NoMemory();
SWIG_fail;
}
resultobj = SWIG_NewPointerObj((new std::string(static_cast< const std::string& >(result))), SWIGTYPE_p_std__string, SWIG_POINTER_OWN | 0 );
return resultobj;
fail:
return NULL;
}
Notice how new std::string has no try catch around it.

Answer 1

The typemap just tells SWIG what interface code to generate to convert call parameters and return value of the function. The %exception generates code immediately before and after the function to be wrapped, to transition exceptions from C++ to target language or to convert the C++ exception to the target language equivalent. If you use %exception as per the SWIG docs, you should find that your wrapper function contains the typemap code you specified for that function, and the exception code around your C++ function:
void swig_function(PyObj*) {
typemap-related code to convert args from Python to C++
exception-related code
your-c++-func(args)
exception-related code (catch clauses etc)
typemap-related code to convert return value from C++ to Python
}