"audiences": ", ".join(book.audiences_pl()),
"audiobook": "audiobook" if book.has_media('mp3') else "",
"children": book_tree_csv(author, books_by_parent.get(book.id, ()), books_by_parent, depth + 1)
"audiences": ", ".join(book.audiences_pl()),
"audiobook": "audiobook" if book.has_media('mp3') else "",
"children": book_tree_csv(author, books_by_parent.get(book.id, ()), books_by_parent, depth + 1)