code: def from_dict(self, subj_files):
          
          for group_label in subj_files:
              try:
                  group_files = subj_files[group_label]
                  self.items.extend([self._load_image(get_abspath(imgf)) for imgf in group_files])
  
                  self.labels.extend([group_label]*len(group_files))
  
              except Exception as exc:
                  raise Exception('Error while reading files from '
                                  'group {0}.'.format(group_label)) from exc
docs: Parameters
          ----------
          subj_files: dict of str
              file_path -> int/str