code: def add_degree_days(self, col='OAT', hdh_cpoint=65, cdh_cpoint=65):
          
  
          if self.preprocessed_data.empty:
              data = self.original_data
          else:
              data = self.preprocessed_data
  
          # Calculate hdh
          data['hdh'] = data[col]
          over_hdh = data.loc[:, col] > hdh_cpoint
          data.loc[over_hdh, 'hdh'] = 0
          data.loc[~over_hdh, 'hdh'] = hdh_cpoint - data.loc[~over_hdh, col]
  
          # Calculate cdh
          data['cdh'] = data[col]
          under_cdh = data.loc[:, col] < cdh_cpoint
          data.loc[under_cdh, 'cdh'] = 0
          data.loc[~under_cdh, 'cdh'] = data.loc[~under_cdh, col] - cdh_cpoint
  
          self.preprocessed_data = data
docs: Adds Heating & Cooling Degree Hours.
  
          Parameters
          ----------
          col         : str
              Column name which contains the outdoor air temperature.
          hdh_cpoint  : int
              Heating degree hours. Defaults to 65.
          cdh_cpoint  : int
              Cooling degree hours. Defaults to 65.