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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 sorted_files_from_bucket(bucket, keys=None):
 """Return files from bucket sorted by given keys. :param bucket: :class:`~invenio_files_rest.models.Bucket` containing the files. :param keys: Keys order to be used. :returns: Sorted list of bucket items. """

    keys = keys or []
    total = len(keys)
    sortby = dict(zip(keys, range(total)))
    values = ObjectVersion.get_by_bucket(bucket).all()
    return sorted(values, key=lambda x: sortby.get(x.key, total))