code: def _list_images(self, root):
          
          self.labels = []
          self.items = []
  
          valid_unseen_sub_idx = [1, 2, 20, 22]
          skip_sub_idx = [21]
  
          if self._mode == 'train':
              sub_idx = ['s' + str(i) for i in range(1, 35) \
                               if i not in valid_unseen_sub_idx + skip_sub_idx]
          elif self._mode == 'valid':
              sub_idx = ['s' + str(i) for i in valid_unseen_sub_idx]
  
          folder_path = []
          for i in sub_idx:
              folder_path.extend(glob.glob(os.path.join(root, i, "*")))
  
          for folder in folder_path:
              filename = glob.glob(os.path.join(folder, "*"))
              if len(filename) != self._seq_len:
                  continue
              filename.sort()
              label = os.path.split(folder)[-1]
              self.items.append((filename, label))
docs: Description : generate list for lip images