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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 _first_of_quarter(self, day_of_week=None):
 """ Modify to the first occurrence of a given day of the week in the current quarter. If no day_of_week is provided, modify to the first day of the quarter. Use the supplied consts to indicate the desired day_of_week, ex. DateTime.MONDAY. :type day_of_week: int or None :rtype: DateTime """

        return self.on(self.year, self.quarter * 3 - 2, 1).first_of(
            "month", day_of_week
        )