code: def add_weeks(self, datetimestr, n, return_date=False):
          
          a_datetime = self.parse_datetime(datetimestr)
          a_datetime += timedelta(days=7 * n)
          if return_date:
              return a_datetime.date()
          else:
              return a_datetime
docs: Returns a time that n weeks after a time.
  
          :param datetimestr: a datetime object or a datetime str
          :param n: number of weeks, value can be negative
          :param return_date: returns a date object instead of datetime
  
          **中文文档**
  
          返回给定日期N周之后的时间。