docs: def cache_valid(self, col):
          """
          Checks whether the column has a factorization that exists and is not older than the source
  
          :param col:
          :return:
          """
          cache_valid = False
  
          if self.rootdir:
              col_org_file_check = self[col].rootdir + '/__attrs__'
              col_values_file_check = self[col].rootdir + '.values/__attrs__'
              cache_valid = os.path.exists(col_org_file_check) and os.path.exists(col_values_file_check)
  
          return cache_valid