Aggregation

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Aggregation in Python, particularly in the context of Object-Oriented Programming (OOP), describes a “has-a” relationship between classes. This means one class contains references to objects of other classes as its attributes, but the contained objects can exist independently of the container object. The lifecycle of the contained objects is not tightly bound to the lifecycle of the container. 

class Library:
    def __init__(self, name):
        self.name = name
        self.books = []

    def add_book(self, book):
        self.books.append(book)

    def list_books(self):
        return [f"{book.title} by {book.author}" for book in self.books]

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

library = Library("New York Public Library")

book1 = Book("Harry Potter...", "J.K. Rowling")
book2 = Book("The Hobbit", "J. R. R. Tolkein")
book3 = Book("The Colour of Magic", "Terry Pratchett")

library.add_book(book1)
library.add_book(book2)
library.add_book(book3)

print(library.name)

for book in library.list_books():
    print(book)

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