code: def filter_by_keyword(self, keyword):
          
          filtered_days = []
          for des_day in self.design_days:
              if keyword in des_day.name:
                  filtered_days.append(des_day)
          return filtered_days
docs: Return a list of ddys that have a certain keyword in their name.
  
          This is useful for selecting out design days from a ddy file that are
          for a specific type of condition (for example, .4% cooling design days)