code: def update_old_names():
      
  
      url = urlparse(ZONEINFO_URL)
      log.info('Connecting to %s' % url.netloc)
      ftp = ftplib.FTP(url.netloc)
      ftp.login()
      gzfile = BytesIO()
  
      log.info('Fetching zoneinfo database')
      ftp.retrbinary('RETR ' + url.path, gzfile.write)
      gzfile.seek(0)
  
      log.info('Extracting backwards data')
      archive = tarfile.open(mode="r:gz", fileobj=gzfile)
      backward = {}
      for line in archive.extractfile('backward').readlines():
          if line[0] == '#':
              continue
          if len(line.strip()) == 0:
              continue
          parts = line.split()
          if parts[0] != b'Link':
              continue
  
          backward[parts[2].decode('ascii')] = parts[1].decode('ascii')
  
      return backward
docs: Fetches the list of old tz names and returns a mapping