code: def add(self, years=0, months=0, weeks=0, days=0):
          
          dt = add_duration(
              date(self.year, self.month, self.day),
              years=years,
              months=months,
              weeks=weeks,
              days=days,
          )
  
          return self.__class__(dt.year, dt.month, dt.day)
docs: Add duration to the instance.
  
          :param years: The number of years
          :type years: int
  
          :param months: The number of months
          :type months: int
  
          :param weeks: The number of weeks
          :type weeks: int
  
          :param days: The number of days
          :type days: int
  
          :rtype: Date