"audiobook": "audiobook" if book.has_media('mp3') else "",
"children": book_tree_texml(books_by_parent.get(book.id, ()), books_by_parent, depth + 1)
} for book in book_list)
"audiobook": "audiobook" if book.has_media('mp3') else "",
"children": book_tree_texml(books_by_parent.get(book.id, ()), books_by_parent, depth + 1)
} for book in book_list)