Getting error message/trace over the C API

[Sami Vaisanen]

On Tue, 16 Oct 2007 18:55:22 +0000, Duncan Booth wrote:

> Sami Vaisanen <ensiferum_ at hotmail.com> wrote:
> 
>> Hello group,
>>  
>> I'm writing a C++ based application that embeds the python engine. Now I
>> have a problem regarding exception/error information. Is there a way to
>> get the exception message and possibly the traceback into a string for
>> example? I've been eyeballing the PyErr_ module and it seems fairly
>> limited. In other words PyErr_Print() calls the right functions for
>> getting the exception information but unfortunately it is hardwired to
>> print this data directly into sys.stderr, and for an embedded application
>> this is completely inappropriate. 
>>  
>>  
>> Please advice how to do this.
>> 
> All you have to do is call whatever functions you would call from Python. 
> e.g. from C you need to import traceback, then call getattr to get the 
> appropriate function (e.g. format_exc or format_exception), then just call 
> it.



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";
}

str evaluates to "None", any ideas what gives here? I've also tried to
call the traceback with a different function, such as
PyObject_CallFunctionObjArgs but the result is still same.

Thanks