code: def _get_offset_day(self, other):
          
          mstart = datetime(other.year, other.month, 1)
          wday = mstart.weekday()
          shift_days = (self.weekday - wday) % 7
          return 1 + shift_days + self.week * 7
docs: Find the day in the same month as other that has the same
          weekday as self.weekday and is the self.week'th such day in the month.
  
          Parameters
          ----------
          other : datetime
  
          Returns
          -------
          day : int