+	PyErr_Fetch(&error_type, &error_value, &error_traceback);
+	
+	PyErr_Clear();

I think that the call to PyErr_Clear() is useless, PyErr_Fetch() already cleared the exception.

+	/* clear the error */
+	PyErr_Restore(error_type, error_value, error_traceback);
+	PyErr_Clear();

Why do you restore the error if you clear it directly? I think that at this position, there is no current exception. So it may be simplified as:

Py_DECREF(error_type);
Py_DECREF(error_value);
Py_DECREF(error_traceback);

I suppose here that all these 3 variables are not NULL.

+	if(! (string_io_mod= PyImport_ImportModule("io")) ) {
+		PyErr_Clear();
+		return NULL;
+	}
+	else if (! (string_io= PyObject_CallMethod(string_io_mod, "StringIO", NULL))) {
+		PyErr_Clear();
+		Py_DECREF(string_io_mod);
+		return NULL;
+	}
+	else if (! (string_io_getvalue= PyObject_GetAttrString(string_io, "getvalue"))) {
+		PyErr_Clear();
+		Py_DECREF(string_io_mod);
+		Py_DECREF(string_io);
+		return NULL;
+	}

Minor style remark: you can remove the "else" keywords here.

You should factorize the error handling at the end using "goto error;" with a error handler looking like:
------------
   ...
   goto finally;

error:
   PyErr_Clear();
   Py_CLEAR(stringio_buf);
finally:
   Py_XDECREF(string_io_mod);
   Py_XDECREF(string_io);
   Py_XDECREF(string_io_getvalue);
   return NULL;
------------
In my opinion, it's easier to maintain it, and more readable.