Gui: fix Gui.addCommand() in Python3

src/Gui/ApplicationPy.cpp

@@ -1144,12 +1144,20 @@ PyObject* Application::sAddCommand(PyObject * /*self*/, PyObject *args)
             return 0;
         }
         Py::Callable inspect(mod.getAttr("stack"));
-        Py::Tuple args;
-        Py::List list(inspect.apply(args));
-        args = list.getItem(0);
+        Py::List list(inspect.apply());
 
+        std::string file;
         // usually this is the file name of the calling script
-        std::string file = args.getItem(1).as_string();
+#if (PY_MAJOR_VERSION > 3 || (PY_MAJOR_VERSION==3 && PY_MINOR_VERSION>=5))
+        Py::Object info = list.getItem(0);
+        PyObject *pyfile = PyStructSequence_GET_ITEM(*info,1);
+        if(!pyfile)
+            throw Py::Exception();
+        file = Py::Object(pyfile).as_string();
+#else
+        Py::Tuple info = list.getItem(0);
+        file = info.getItem(1).as_string();
+#endif
         Base::FileInfo fi(file);
         // convert backslashes to slashes
         file = fi.filePath();