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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_weeks(self, datetimestr, n, return_date=False):
 """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。 """

        a_datetime = self.parse_datetime(datetimestr)
        a_datetime += timedelta(days=7 * n)
        if return_date:
            return a_datetime.date()
        else:
            return a_datetime