docs: def bz2_opener(path, pattern='', verbose=False):
      """Opener that opens single bz2 compressed file.
  
      :param str path: Path. 
      :param str pattern: Regular expression pattern.
      :return: Filehandle(s).
      """
      source = path if is_url(path) else os.path.abspath(path)
      filename = os.path.basename(path)
  
      if pattern and not re.match(pattern, filename):
          logger.verbose('Skipping file: {}, did not match regex pattern "{}"'.format(os.path.abspath(path), pattern))
          return
  
      try:
          filehandle = bz2.open(io.BytesIO(urlopen(path).read())) if is_url(path) else bz2.open(path)
          filehandle.read(1)
          filehandle.seek(0)
          logger.verbose('Processing file: {}'.format(source))
          yield filehandle
      except (OSError, IOError):
          raise BZ2ValidationError