python处理几年前几月前几日前的时间

def conv_time(t):
    min = int(re.findall('d+', t)[0])
    print(min,'---')
    dt = arrow.now()
    if u'秒' in t:
        s = (dt - timedelta(seconds=min))
    elif u'分钟' in t:
        s = (dt - timedelta(minutes=min))

    elif u'小时' in t:
        s = (dt - timedelta(hours=min))
    elif u'天' in t:
        s = (dt - timedelta(days=min))
    elif u'周' in t:
        s = (dt - timedelta(weeks=min))
    elif u'月' in t:
        s = dt.shift(months=-min)
    elif u'年' in t:
        s =str(int(datetime.datetime.now().strftime("%Y"))-min)+"-"+datetime.datetime.now().strftime("%m-%d")
    else:
        t += ", " + current_year
        s = datetime.strptime(t, "%m-%d, %Y")
    return int(time.mktime(s.timetuple()))