python 输出上个月的月末日期

import  dateutildef before_month_lastday(ti):    today=dateutil.parser.parse(str(ti))    first = datetime.date(day=1, month=today.month, year=today.year)    lastMonth = first - datetime.timedelta(days=1)    cc=str(lastMonth.year)+str(lastMonth.month)+str(lastMonth.day)    return int(cc)print(before_month_lastday(20171011))

2017930