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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_hours(self, datetimestr, n):
 """Returns a time that n hours after a time. :param datetimestr: a datetime object or a datetime str :param n: number of hours, value can be negative **中文文档** 返回给定日期N小时之后的时间。 """

        a_datetime = self.parse_datetime(datetimestr)
        return a_datetime + timedelta(seconds=3600 * n)