Extending Python with C API

Sami Vaisanen ensiferum_ at hotmail.com
Fri Oct 19 00:45:23 CEST 2007

On Thu, 13 Sep 2007 21:26:33 -0400, Carsten Haese wrote:

> On Thu, 2007-09-13 at 18:05 -0700, Thierry Masson wrote:
>> Hello,
>> I'm trying to use the C API to extend Python. I've looked at various
>> books and web sites (including the docs at python.org) and I can't get
>> any of the samples to work. Below is a very minimalist example that
>> I'm trying to get working and I was wondering if someone could tell me
>> where I'm going wrong. It's probably something very obvious to those
>> familiar with this technique. 
>> The setup script builds the library OK, and I've verified that
>> gtestmodule.so is getting created. But when I try to run a test script
>> ( test.py, above) that uses the library, I get this error:
>> Traceback (most recent call last):
>>   File "test.py", line 2, in ?
>>     import gtestmodule
>> ImportError: ./gtestmodule.so: undefined symbol: PyBuildValue 
> Your module C code uses an unknown function by the name of PyBuildValue.
> The actual name of the function you mean is Py_BuildValue.
> HTH,

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);
            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";
    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.


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