traceback over C API and PyObject_CallObject

[Sami Vaisanen]

Hello group,

I'm trying to get the Python exception information (message and traceback)
stored into a string in my C++ code. However all i get back is the string
"None". All the checks pass and all pointers get a value from the python
API calls. I've also tried with a different function such as
PyObject_CallFunctionObjArgs but the result is the same.

Thanks

void get_python_exception(string& message, string& traceback)
{
GIL g;

PyObject* type = NULL;
PyObject* value = NULL;
PyObject* trace = NULL;

PyErr_Fetch(&type, &value, &trace);

py_ref ref_type(type);
py_ref ref_value(value);
py_ref ref_trace(trace);

py_ref name(PyString_FromString("traceback"));
py_ref module(PyImport_Import(name.get()));
if (module)
{
py_ref fun(PyObject_GetAttrString(module.get(), "format_exc"));
if (fun)
{
PyErr_Restore(type, value, trace);
ref_type.release();
ref_value.release();
ref_trace.release();

py_ref ret(PyObject_CallObject(fun.get(), NULL));
if (ret && PyString_Check(ret.get()))
{
char* str = PyString_AsString(ret.get());
message = str;
traceback = "traceback not available";
return;
}
}
}
message = "message not available";
traceback = "traceback not available";
}

 

[Gabriel Genellina]

Hello group,

I'm trying to get the Python exception information (message and
traceback)
stored into a string in my C++ code. However all i get back is the string
"None".

This is what you get (actually "None\n") when there is no error set.

All the checks pass and all pointers get a value from the python
API calls. I've also tried with a different function such as
PyObject_CallFunctionObjArgs but the result is the same.

Since you already know the three components (type, value, trace), I'd use
traceback.format_exception instead (and remove the PyErr_Restore call -
I'm unsure if it works the way you expect it).
In this case you have to pass three arguments, so yes, use
PyObject_CallFunctionObjArgs (remember the final NULL). Beware:
format_exception returns a formatted list, not a string. You have to
concatenate all the elements (either using ''.join or repeteadly calling
PyString_Concat)