input: Write a function that provides a command-line interface for downloading subtitles for movies and TV shows. The function should accept one or more release paths as arguments and allow the user to specify the language and subtitle site. The function should support the following commands: "download", "exist", "test", "list", "help", and "version".
  
  Example usage:
  
  def download_subtitles(releases, engines=[DEFAULTS['subtitle_engine']], lang=DEFAULTS['subtitle_language']):
      if releases:
          for release in releases:
              for engine in engines:
                  subtitle_release = SubtitleSite.get_file_properties(release)['release_name']
                  print "[{engine: ^15}] Trying To Download Subtitles For: '{release}'".format(engine=engine,
                                                                                               release=subtitle_release)
                  sub_obj = SubtitleSite.class_factory(engine)
                  subtitle_path = sub_obj.download_subtitle(release, lang)
                  if subtitle_path:
                      print "{0:17} Download Success: ({file_path}).\n".format("", file_path=subtitle_path)
                  else:
                      print "{0:17} Subtitles Not Found.\n".format("")
  
  def is_subtitles_exist(releases, engines=[DEFAULTS['subtitle_engine']], lang=DEFAULTS['subtitle_language']):
      if releases:
          for release in releases:
              for engine in engines:
                  subtitle_release = SubtitleSite.get_file_properties(release)['release_name']
  
                  sub_obj = SubtitleSite.class_factory(engine)
                  exist_flag = sub_obj.is_subtitle_exist(release, lang)
                  res = "Exist"
                  if not exist_flag:
                      res = "Does Not " + res
                  print "[{engine: ^15}] '{release}' - {res}.".format(engine=engine,
                                                                      release=subtitle_release,
                                                                      res=res)
  
  def test_engines(engines):
      if not engines:
          engines = SUBTITLE_SITE_LIST.keys()
  
      for engine_key in engines:
          t = SubtitleSite.class_factory(engine_key)
          t.test_engine()
  
  assert download_subtitles(["movie1.mp4"], ["opensubtitles"], "en") == "[{opensubtitles: ^15}] Trying To Download Subtitles For: 'movie1.mp4' Download Success: (movie1.srt).\n"
  assert is_subtitles_exist(["movie1.mp4"], ["opensubtitles"], "en") == "[{opensubtitles: ^15}] 'movie1.mp4' - Exist."
  assert test_engines(["opensubtitles"]) == None
  assert list_commands() == ["download", "exist", "test", "list", "help", "version"]
  
output: def download_subtitles(releases, engines=[DEFAULTS['subtitle_engine']], lang=DEFAULTS['subtitle_language']):
      if releases:
          for release in releases:
              for engine in engines:
                  subtitle_release = SubtitleSite.get_file_properties(release)['release_name']
                  print("[{engine: ^15}] Trying To Download Subtitles For: '{release}'".format(engine=engine, release=subtitle_release))
                  sub_obj = SubtitleSite.class_factory(engine)
                  subtitle_path = sub_obj.download_subtitle(release, lang)
                  if subtitle_path:
                      print("{0:17} Download Success: ({file_path}).\n".format("", file_path=subtitle_path))
                  else:
                      print("{0:17} Subtitles Not Found.\n".format(""))
  
  def is_subtitles_exist(releases, engines=[DEFAULTS['subtitle_engine']], lang=DEFAULTS['subtitle_language']):
      if releases:
          for release in releases:
              for engine in engines:
                  subtitle_release = SubtitleSite.get_file_properties(release)['release_name']
                  sub_obj = SubtitleSite.class_factory(engine)
                  exist_flag = sub_obj.is_subtitle_exist(release, lang)
                  res = "Exist"
                  if not exist_flag:
                      res = "Does Not " + res
                  print("[{engine: ^15}] '{release}' - {res}.".format(engine=engine, release=subtitle_release, res=res))
  
  def test_engines(engines):
      if not engines:
          engines = SUBTITLE_SITE_LIST.keys()
      for engine_key in engines:
          t = SubtitleSite.class_factory(engine_key)
          t.test_engine()
  
  def list_commands():
      return ["download", "exist", "test", "list", "help", "version"]