def METHOD_NAME(self, filename, v_pos, t_pos_idx, v_tex, t_tex_idx):
    with open(filename, 'w') as f:
        for v in v_pos:
            f.write('v {} {} {} \n'.format(v[0], v[1], v[2]))
        if v_tex is not None:
            assert (len(t_pos_idx) == len(t_tex_idx))
            for v in v_tex:
                f.write('vt {} {} \n'.format(v[0], 1.0 - v[1]))
        for i in range(len(t_pos_idx)):
            f.write('f ')
            for j in range(3):
                f.write(
                    ' %s/%s' %
                    (str(t_pos_idx[i][j] + 1),
                     '' if v_tex is None else str(t_tex_idx[i][j] + 1)))
            f.write('\n')