How to use the crontab.CronItem.from_line function in crontab

def schedule_cron(command, interval, crontab=None):
    from crontab import CronTab, CronItem
    if not os.path.exists(crontab):
        with open(crontab, 'w'):
            pass

    if crontab:
        c = CronTab(tabfile=crontab)
    else:
        c = CronTab(user=getpass.getuser())

    job = CronItem.from_line(interval + ' ' + command, cron=c)

    c.append(job)
    c.write()
    return c, job