Library Problem [Non-ordinary Solution]

main.py

class Book:
    def __init__(self, title, genre):
        self.title = title
        self.genre = genre


class LibraryShelves(dict):
    def add_shelf(self, new_genre: str):
        """Adds a new shelf to library"""
        if new_genre not in self:
            self[new_genre] = list()
        return self

    def remove_shelf(self, genre: str):
        """Removes the shelf from library. if it exists"""
        if genre in self:
            self.pop(genre)
        return self


class Library:
    __instances = dict()

    def __new__(cls, *args, **kwargs):
        library_name = kwargs.get('library_name')

        if library_name not in cls.__instances:
            new_instance = super().__new__(cls)

            cls.__instances[library_name] = new_instance
            return new_instance
        else:
            return cls.__instances[library_name]

    def __init__(self, library_name: str):

        if not hasattr(self, 'shelves'):
            self.shelves = LibraryShelves()

        self.library_name = library_name

    def add_book(self, book: Book):
        book_genre = book.genre

        if book_genre in self.shelves:
            self.shelves[book_genre].append(book)
        else:
            self.shelves[book_genre] = [book]
        return self

    def add_books(self, books: list[Book]):
        for book in books:
            self.add_book(book=book)
        return self

    @property
    def get_all_books(self) -> dict:
        return self.shelves

    def get_books_by_genra(self, genra: str) -> list:
        return self.shelves[genra] if genra in self.shelves else []


if __name__ == '__main__':
    book1 = Book(title="Harry Potter", genre="Fantasy")
    book2 = Book(title="Lord of the rings", genre="Fantasy")

    ny_library = Library(library_name="New York National Library")
    tokyo_library = Library(library_name="Tokyo National Library")

    ny_library.add_books([book1, book2])
    tokyo_library.add_book(book1)

    duplicate_ny_library = Library(library_name="New York National Library")

    print(ny_library.get_all_books)  # dict[str:list[Book, Book]]
    print(tokyo_library.get_all_books)  # dict[str:list[Book]]
    print(id(duplicate_ny_library) == id(ny_library))  # True