code: def _to_ctfile_atom_block(self, key):
          
          counter = OrderedCounter(Atom.atom_block_format)
          ctab_atom_block = '\n'.join([''.join([str(value).rjust(spacing) for value, spacing
                                                in zip(atom._ctab_data.values(), counter.values())])
                                       for atom in self[key]])
          return '{}\n'.format(ctab_atom_block)
docs: Create atom block in `CTfile` format.
  
          :param str key: Ctab atom block key. 
          :return: Ctab atom block.
          :rtype: :py:class:`str`