code: def nth_of(self, unit, nth, day_of_week):
          
          if unit not in ["month", "quarter", "year"]:
              raise ValueError('Invalid unit "{}" for first_of()'.format(unit))
  
          dt = getattr(self, "_nth_of_{}".format(unit))(nth, day_of_week)
          if dt is False:
              raise PendulumException(
                  "Unable to find occurence {} of {} in {}".format(
                      nth, self._days[day_of_week], unit
                  )
              )
  
          return dt
docs: Returns a new instance set to the given occurrence
          of a given day of the week in the current unit.
          If the calculated occurrence is outside the scope of the current unit,
          then raise an error. Use the supplied consts
          to indicate the desired day_of_week, ex. DateTime.MONDAY.
  
          Supported units are month, quarter and year.
  
          :param unit: The unit to use
          :type unit: str
  
          :type nth: int
  
          :type day_of_week: int or None
  
          :rtype: DateTime