code: def get_digest_keys(self):
          
  
          digest_keys = []
          for col in xrange(self.GetNumberCols()):
              digest_key = self.GetCellValue(self.has_header, col)
              if digest_key == "":
                  digest_key = self.digest_types.keys()[0]
              digest_keys.append(digest_key)
  
          return digest_keys
docs: Returns a list of the type choices