Python Iterator

To make a class iterable you must implement the iterator methods __iter__ and __next__.

class Book:
    def __init__(self, name: str, author: str, page_count: int):
        self.name = name
        self.author = author
        self.page_count = page_count
 
class Bookshelf:
    def __init__(self):
        self._books = []
 
    def add_book(self, book: Book):
        self._books.append(book)
 
    # This is the iterator initialization method
    # The iteration variable(s) should be initialized here
    def __iter__(self):
        self.n = 0
        # the method returns a reference to the object itself as 
        # the iterator is implemented within the same class definition
        return self
 
    # This method returns the next item within the object
    # If all items have been traversed, the StopIteration event is raised
    def __next__(self):
        if self.n < len(self._books):
            # Select the current item from the list within the object
            book = self._books[self.n]
            # increase the counter (i.e. iteration variable) by one
            self.n += 1
            # return the current item
            return book
        else:
            # All books have been traversed
            raise StopIteration