Python 类定义 图书管理系统

好的，以下是一个简单的Python类定义，用于图书管理系统的示例。这个示例包括几个类，如`Book`、`User`和`Library`，以及它们的基本方法和属性。

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

    def __str__(self):
        return f"《{self.title}》 by {self.author}, ISBN: {self.isbn}"

    def borrow_book(self):
        if self.is_available:
            self.is_available = False
            return True
        else:
            return False

    def return_book(self):
        self.is_available = True


class User:
    def __init__(self, user_id, name):
        self.user_id = user_id
        self.name = name
        self.borrowed_books = []

    def borrow_book(self, book):
        if book.borrow_book():
            self.borrowed_books.append(book)
            print(f"{self.name} 成功借阅了 {book.title}")
        else:
            print(f"{book.title} 已经被借走了")

    def return_book(self, book):
        if book in self.borrowed_books:
            book.return_book()
            self.borrowed_books.remove(book)
            print(f"{self.name} 成功归还了 {book.title}")
        else:
            print(f"{self.name} 没有借阅过 {book.title}")


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

    def add_book(self, book):
        self.books.append(book)
        print(f"添加了新书: {book}")

    def register_user(self, user):
        self.users.append(user)
        print(f"注册了新用户: {user.name}")

    def find_book_by_title(self, title):
        for book in self.books:
            if book.title == title:
                return book
        return None

    def find_user_by_id(self, user_id):
        for user in self.users:
            if user.user_id == user_id:
                return user
        return None


# 示例使用
library = Library()

# 添加书籍
library.add_book(Book("Python编程", "John Doe", "1234567890"))
library.add_book(Book("数据科学导论", "Jane Smith", "0987654321"))

# 注册用户
library.register_user(User("001", "Alice"))
library.register_user(User("002", "Bob"))

# 查找书籍
book = library.find_book_by_title("Python编程")
user = library.find_user_by_id("001")

# 借阅书籍
user.borrow_book(book)

# 归还书籍
user.return_book(book)

在这个示例中，`Book`类表示一本书，`User`类表示一个用户，`Library`类表示整个图书馆。`Library`类包含添加书籍、注册用户、查找书籍和用户的方法。`User`类包含借阅和归还书籍的方法。