帮我写一个简单的在库管理系统

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

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

    def display_books(self):
        for book in self.books:
            print(book)

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

    def __str__(self):
        return f"{self.title} by {self.author}"

# 创建一个图书馆实例
library = Library()

# 添加书籍
book1 = Book("Python编程入门", "张三")
book2 = Book("Java实践指南", "李四")
library.add_book(book1)
library.add_book(book2)

# 显示所有书籍
library.display_books()