On 31/07/12 21:14, Glenn Ramsey wrote:
Using boost::python how can I create an a custom exception that is derived from
Python's Exception? The functionality I would like to get by doing this is to
provide additional methods for the catching code to retrieve information from
the exception.
I know it is possible to just wrap and throw my own exception class but it seems
that because it is not derived from Exception then in certain situations I get
the error "SystemError: 'finally' pops bad exception".
This example [1] shows how to wrap a C++ exception class...
class MyCPPException : public std::exception {...}
using namespace boost::python;
...
PyObject *myCPPExceptionType=0;
void translate(MyCPPException const &e)
{
PyErr_SetObject(myCPPExceptionType, object(e).ptr());
}
BOOST_PYTHON_MODULE(MyModule)
{
...
class_<MyCPPException> myCPPExceptionClass("MyCPPException"...);
myCPPExceptionClass
.def("get_extra_info", &MyCPPException::get_extra_info);
myCPPExceptionType=myCPPExceptionClass.ptr();
register_exception_translator<MyCPPException>(&translate);
...
}
But this is not derived from Exception.
This example [2] shows how to create an exception that is derived from
Exception.
PyObject* createExceptionClass(const char* name, PyObject* baseTypeObj =
PyExc_Exception)
{
using std::string;
namespace bp = boost::python;
string scopeName = bp::extract<string>(bp::scope().attr("__name__"));
string qualifiedName0 = scopeName + "." + name;
char* qualifiedName1 = const_cast<char*>(qualifiedName0.c_str());
PyObject* typeObj = PyErr_NewException(qualifiedName1, baseTypeObj, 0);
if(!typeObj) bp::throw_error_already_set();
bp::scope().attr(name) = bp::handle<>(bp::borrowed(typeObj));
return typeObj;
}
PyObject* myExceptionTypeObj = 0;
void translate(MyCPPException const &e)
{
PyErr_SetObject(myExceptionTypeObj, object(e).ptr());
}
BOOST_PYTHON_MODULE(MyModule)
{
register_exception_translator<MyCPPException>(&translateFunc);
...
myExceptionTypeObj = createExceptionClass("MyException");
...
}
But this doesn't have any custom methods to get info from the exception.
How can I do both at the same time?
Glenn
[2]
<http://stackoverflow.com/questions/9620268/boost-python-custom-exception-class>
[1]
<http://stackoverflow.com/questions/2261858/boostpython-export-custom-exception>
Forgot to mention a couple of things that I tried already...
Passing a tuple of PyExc_Exception and my wrapped custom exception to
PyErr_NewException, for multiple inheritance, caused an error when attempting to
load the module in Python, something about incompatible types.
Extracting __dict__ from my wrapped custom exception and passing it to
PyErr_NewException also caused an error when attempting load the module. I don't
have it in front of me now but it was complaining about wanting dict instead of
dictproxy.
Glenn
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