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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 prev_period(self):
 """ The period before this range. PeriodRange([datetime.date(1999, 12, 1),datetime.date(2000, 1, 1))) :return: A new :class:`~spans.types.PeriodRange` for the period before this period """


        return self.from_date(self.prev(self.lower), period=self.period)