# library_management.py  
# 导入必要的模块  
import os  
  
# 定义存储图书信息的文件路径  
BOOK_FILE = 'books.txt'

class Book:  
    def __init__(self, title, author, isbn, year_published):  
        """  
        初始化Book对象  
        :param title: 书名  
        :param author: 作者  
        :param isbn: ISBN号  
        :param year_published: 出版年份  
        """  
        self.title = title  
        self.author = author  
        self.isbn = isbn  
        self.year_published = year_published  
  
    def __str__(self):  
        """  
        定义Book对象的字符串表示形式  
        :return: 格式化后的书籍信息字符串  
        """  
        return f"{self.title} by {self.author} ({self.year_published}), ISBN: {self.isbn}"

class Library:  
    def __init__(self):  
        """  
        初始化Library对象，并加载已有的图书信息  
        """  
        self.books = []  
        self.load_books()  
  
    def load_books(self):  
        """  
        从文件中加载图书信息  
        """  
        if os.path.exists(BOOK_FILE):  
            with open(BOOK_FILE, 'r') as file:  
                for line in file:  
                    book_info = line.strip().split(',')  
                    book = Book(book_info[0], book_info[1], book_info[2], book_info[3])  
                    self.books.append(book)  
  
    def add_book(self, book):  
        """  
        添加新书到图书馆  
        :param book: 要添加的Book对象  
        """  
        self.books.append(book)  
        self.save_books()  
  
    def save_books(self):  
        """  
        将图书信息保存到文件中  
        """  
        with open(BOOK_FILE, 'w') as file:  
            for book in self.books:  
                file.write(f"{book.title},{book.author},{book.isbn},{book.year_published}\n")  
  
    def display_books(self):  
        """  
        显示所有书籍信息  
        """  
        for book in self.books:  
            print(book)  
  
    def find_book_by_title(self, title):  
        """  
        根据书名查找书籍  
        :param title: 要查找的书名  
        :return: 找到的Book对象列表  
        """  
        return [book for book in self.books if book.title.lower() == title.lower()]  
  
    def find_book_by_author(self, author):  
        """  
        根据作者查找书籍  
        :param author: 要查找的作者名  
        :return: 找到的Book对象列表  
        """  
        return [book for book in self.books if book.author.lower() == author.lower()]

def main():  
    library = Library()  
  
    while True:  
        print("\n图书管理系统")  
        print("1. 添加新书")  
        print("2. 显示所有书籍")  
        print("3. 按书名查找书籍")  
        print("4. 按作者查找书籍")  
        print("5. 退出")  
        choice = input("请选择操作: ")  
  
        if choice == '1':  
            title = input("请输入书名: ")  
            author = input("请输入作者: ")  
            isbn = input("请输入ISBN号: ")  
            year_published = input("请输入出版年份: ")  
            book = Book(title, author, isbn, year_published)  
            library.add_book(book)  
            print("新书添加成功！")  
  
        elif choice == '2':  
            library.display_books()  
  
        elif choice == '3':  
            title = input("请输入要查找的书名: ")  
            books = library.find_book_by_title(title)  
            if books:  
                for book in books:  
                    print(book)  
            else:  
                print("未找到该书。")  
  
        elif choice == '4':  
            author = input("请输入要查找的作者: ")  
            books = library.find_book_by_author(author)  
            if books:  
                for book in books:  
                    print(book)  
            else:  
                print("未找到该作者的书籍。")  
  
        elif choice == '5':  
            print("退出系统。")  
            break  
  
        else:  
            print("无效选择，请重新输入。")  
  
if __name__ == "__main__":  
    main()