code: def get_bbl(arxiv_id):
      
      tar_file = get_sources(arxiv_id)
      bbl_files = [i for i in tar_file.getmembers() if i.name.endswith(".bbl")]
      bbl_files = [tar_file.extractfile(member).read().decode(tarfile.ENCODING)
                   for member in bbl_files]
      return bbl_files
docs: Get the .bbl files (if any) of a given preprint.
  
      .. note::
  
          Bulk download of sources from arXiv is not permitted by their API. \
                  You should have a look at http://arxiv.org/help/bulk_data_s3.
  
      :param arxiv_id: The arXiv id (e.g. ``1401.2910`` or ``1401.2910v1``) in \
              a canonical form.
      :returns: A list of the full text of the ``.bbl`` files (if any) \
              or ``None``.