import datetime

def get_month_zone(before_day):
    today = datetime.date.today()
    day = today.day
    year = today.year
    month = today.month
    if day > before_day:
        last_day = today-datetime.timedelta(1)
        first_day = datetime.date(datetime.date.today().year,datetime.date.today().month,1)

    else:
        last_day = datetime.date(year,month,1)-datetime.timedelta(1)
        first_day = datetime.date(last_day.year,last_day.month,1)
    return [first_day, last_day]
time_zone  = get_month_zone(16)
print('时间区间：{}-----{}'.format(time_zone[0].strftime("%Y-%m-%d"), time_zone[1].strftime(("%Y-%m-%d"))))