上周某一天

import datatime
import calendar
def get_last_sunday(time):
    """
    datatime ->str
    返回上周的星期天
    """
    oneday = datetime.timedelta(days=1)
    if time.weekday() ==calendar.SUNDAY:　　#要星期几，就选星期几
        time=time-oneday
    while time.weekday() != calendar.SUNDAY:
        time -= oneday
    return time.strftime('%Y-%m-%d')