input: Write a function to implement a command-line interface for downloading subtitles for movies and TV shows. The function should include commands to download subtitles, check if subtitles exist, test subtitle engines, list available engines, and display help and version information. The function should take one or more release paths as arguments, and optionally allow specifying the language and subtitle site to use. The available commands are "download", "exist", "test", "list", "help", and "version".
  
  
  def main():
      args = docopt(__doc__, help=True, version='Subtitles Client %s' % __version__)
  
      if args['download']:
          download_subtitles(args['<releases_path>'], args['--engine'], args['--lang'])
      elif args['exist']:
          is_subtitles_exist(args['<releases_path>'], args['--engine'], args['--lang'])
      elif args['test']:
          test_engines(args['<engines>'])
      elif args['--list']:
          for sub_site in SUBTITLE_SITE_LIST.keys():
              sub_dict = SUBTITLE_SITE_LIST.get(sub_site)
              print sub_dict.get('class_name')
  
  
  assert download_subtitles(['path/to/movie'], ['opensubtitles'], 'en')==None
  assert is_subtitles_exist(['path/to/movie'], ['opensubtitles'], 'en')==None
  assert test_engines(['opensubtitles'])==None
  assert main(['-l'])==None
  assert main(['-h'])==None
  assert main(['-v'])==None
output: 
  def main():
      args = docopt(__doc__, help=True, version='Subtitles Client %s' % __version__)
  
      if args['download']:
          download_subtitles(args['<releases_path>'], args['--engine'], args['--lang'])
      elif args['exist']:
          is_subtitles_exist(args['<releases_path>'], args['--engine'], args['--lang'])
      elif args['test']:
          test_engines(args['<engines>'])
      elif args['--list']:
          for sub_site in SUBTITLE_SITE_LIST.keys():
              sub_dict = SUBTITLE_SITE_LIST.get(sub_site)
              print(sub_dict.get('class_name'))
      elif args['help']:
          print(__doc__)
      elif args['version']:
          print('Subtitles Client %s' % __version__)
  