save fence points to a file

def save(self, filename):
        '''save fence points to a file'''
        f = open(filename, mode='w')
        for p in self.rally_points:
            f.write("RALLY %f\t%f\t%f\t%f\t%f\t%d\n" % (p.lat * 1e-7, p.lng * 1e-7, p.alt,
                                                        p.break_alt, p.land_dir, p.flags))
        f.close()