aggregation.py

class Book:

    def __init__(self, name, author, publisher):
        self.name = name
        self.author = author
        self.publisher = publisher

    def book_details(self):
        return f'{self.name} by {self.author} from {self.publisher}'


class Chapter:

    def __init__(self, title, chap_num, book_obj):
        self.title = title
        self.chap_num = chap_num
        self.book_obj = book_obj

    def chapter_details(self):
        return f'Chapter {self.chap_num}: {self.title}, is taken from {self.book_obj.book_details()}'


# Creating Book object
book_obj = Book('Best Book', 'RD', 'RD-pubs')

# Passing Book object to Chapter Book
first_chap = Chapter('Composition', 1, book_obj)

print(first_chap.chapter_details())

# accessing class Book properties and methods using Chapter  Class object
print(first_chap.book_obj.author)
print(first_chap.book_obj.book_details())