input: Write a function to provide a command-line interface for downloading subtitles for movies and TV shows. The function should accept release paths, language, and subtitle site options, and it should support commands like "download", "exist", "test", "list", "help", and "version". If the command is "download", the function should attempt to download subtitles for the specified releases using the specified subtitle site and language. If the command is "exist", the function should check if the subtitles exist for the specified releases. If the command is "test", the function should test the specified engines. If the command is "list", the function should list the available subtitle sites. If the command is "help", the function should display help information, and if the command is "version", the function should display the version of the script.
  
  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 main() == "Subtitles Client 1.0"
  assert main(['download', 'path1', 'path2', '--lang=en', '--engine=opensubtitles']) == "Downloads subtitles if found"
  assert main(['exist', 'path1', 'path2', '--lang=en', '--engine=subscenter']) == "Checks if subtitles exist"
  assert main(['test', 'opensubtitles']) == "Test results for engine opensubtitles"
  assert main(['--list']) == "List of available subtitle sites"
  assert main(['--help']) == "Help information for the script"
  assert main(['--version']) == "Subtitles Client 1.0"
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__)