How to use the epitran.exceptions.MappingError function in epitran

orth, phon = next(reader)
            if orth != 'Orth' or phon != 'Phon':
                raise DatafileError('Header is ["{}", "{}"] instead of ["Orth", "Phon"].'.format(orth, phon))
            for (i, fields) in enumerate(reader):
                try:
                    graph, phon = fields
                except ValueError:
                    raise DatafileError('Map file is not well formed at line {}.'.format(i + 2))
                graph = unicodedata.normalize('NFD', graph)
                phon = unicodedata.normalize('NFD', phon)
                g2p[graph].append(phon)
                gr_by_line[graph].append(i)
        if self._one_to_many_gr_by_line_map(g2p):
            graph, lines = self._one_to_many_gr_by_line_map(gr_by_line)
            lines = [l + 2 for l in lines]
            raise MappingError('One-to-many G2P mapping for "{}" on lines {}'.format(graph, ', '.join(map(str, lines))).encode('utf-8'))
        return g2p