Make sure the next objects to be tallied are compatible with the
        stored trace.

def _check_compatibility(self):
        """Make sure the next objects to be tallied are compatible with the
        stored trace."""
        stored_descr = self._file_trace_description()
        try:
            for k, v in self._model_trace_description():
                assert(stored_descr[k][0] == v[0])
        except:
            raise ValueError(
                "The objects to tally are incompatible with the objects stored in the file.")