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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def download_best_subtitles(videos, languages, min_score=0, hearing_impaired=False, only_one=False, compute_score=None, pool_class=ProviderPool, **kwargs):
 """List and download the best matching subtitles. The `videos` must pass the `languages` and `undefined` (`only_one`) checks of :func:`check_video`. :param videos: videos to download subtitles for. :type videos: set of :class:`~subliminal.video.Video` :param languages: languages to download. :type languages: set of :class:`~babelfish.language.Language` :param int min_score: minimum score for a subtitle to be downloaded. :param bool hearing_impaired: hearing impaired preference. :param bool only_one: download only one subtitle, not one per language. :param compute_score: function that takes `subtitle` and `video` as positional arguments, `hearing_impaired` as keyword argument and returns the score. :param pool_class: class to use as provider pool. :type pool_class: :class:`ProviderPool`, :class:`AsyncProviderPool` or similar :param \*\*kwargs: additional parameters for the provided `pool_class` constructor. :return: downloaded subtitles per video. :rtype: dict of :class:`~subliminal.video.Video` to list of :class:`~subliminal.subtitle.Subtitle` """

    downloaded_subtitles = defaultdict(list)

    # check videos
    checked_videos = []
    for video in videos:
        if not check_video(video, languages=languages, undefined=only_one):
            logger.info('Skipping video %r', video)
            continue
        checked_videos.append(video)

    # return immediately if no video passed the checks
    if not checked_videos:
        return downloaded_subtitles

    # download best subtitles
    with pool_class(**kwargs) as pool:
        for video in checked_videos:
            logger.info('Downloading best subtitles for %r', video)
            subtitles = pool.download_best_subtitles(pool.list_subtitles(video, languages - video.subtitle_languages),
                                                     video, languages, min_score=min_score,
                                                     hearing_impaired=hearing_impaired, only_one=only_one,
                                                     compute_score=compute_score)
            logger.info('Downloaded %d subtitle(s)', len(subtitles))
            downloaded_subtitles[video].extend(subtitles)

    return downloaded_subtitles