code: def _preprocess_request(self, save_data, return_data):
          
          if not self.is_valid_request():
              raise ValueError('Cannot obtain data because request is invalid')
  
          if save_data and self.data_folder is None:
              raise ValueError('Request parameter `data_folder` is not specified. '
                               'In order to save data please set `data_folder` to location on your disk.')
  
          for download_request in self.download_list:
              download_request.set_save_response(save_data)
              download_request.set_return_data(return_data)
              download_request.set_data_folder(self.data_folder)
  
          if save_data:
              for folder in self.folder_list:
                  make_folder(os.path.join(self.data_folder, folder))
docs: Prepares requests for download and creates empty folders
  
          :param save_data: Tells whether to save data or not
          :type: bool
          :param return_data: Tells whether to return data or not
          :type: bool