code: def _data_block(stream):
      
      while len(stream) > 0:
          line = stream.popleft()
  
          if line.startswith('>'):
              yield DataHeader(line[1:].strip())
          else:
              data_item = line.strip()
              if data_item:
                  yield DataItem(line)
              else:
                  continue
docs: Process data block of ``CTfile``.
      
      :param stream: Queue containing lines of text.
      :type stream: :py:class:`collections.deque`
      :return: Tuples of data.
      :rtype: :class:`~ctfile.tokenizer.DataHeader` or :class:`~ctfile.tokenizer.DataItem`