在图书馆借阅系统中逻辑删除图书但是保留借阅记录怎么通过代码实现，有哪些代码

在图书馆借阅系统中，逻辑删除图书并保留借阅记录可以通过以下步骤实现：

1. 在`Book`类中添加一个名为`is_deleted`的属性，用于标记该书籍是否已被删除。默认为`False`。
2. 在`Library`类中的`borrow_book`方法中，添加一个条件判断，如果该书籍已被删除，则提示用户该书籍已下架，无法借阅。
3. 在`Library`类中添加一个名为`delete_book`的方法，用于逻辑删除图书。该方法接受一个参数`book`，表示要删除的书籍。该方法将`book`的`is_deleted`属性设置为`True`，表示该书籍已被删除。
4. 在`Library`类中的`borrowed_books`属性中保留借阅记录，即使该书籍已被删除。这可以通过将`borrowed_books`属性的数据结构修改为一个字典（或其他映射类型），其中键为书籍对象，值为借阅该书籍的用户列表。当逻辑删除图书时，只需将该书籍从`books`列表中移除，不需要将其从`borrowed_books`列表中移除。
5. 在`Library`类中添加一个名为`get_borrowed_books`的方法，用于获取某个用户借阅的所有书籍。该方法接受一个参数`user`，表示要查询的用户。该方法遍历`borrowed_books`字典，找到该用户借阅的所有书籍，并将它们添加到一个列表中返回。

以下是实现上述功能的Python代码示例：

class Book:
    def __init__(self, book_name, author_name, book_ID):
        self.book_name = book_name
        self.author_name = author_name
        self.book_ID = book_ID
        self.is_deleted = False

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

    def borrow_book(self, book, user):
        if book.is_deleted:
            print("Sorry, this book has been removed from the library.")
            return
        if book in self.borrowed_books and user in self.borrowed_books[book]:
            print("Sorry, you have already borrowed this book.")
            return
        if len(user.borrowed_books) >= 3:
            print("Sorry, you have reached the maximum number of borrowed books.")
            return
        self.books.remove(book)
        if book in self.borrowed_books:
            self.borrowed_books[book].append(user)
        else:
            self.borrowed_books[book] = [user]
        user.borrowed_books.append(book)
        print("Book borrowed successfully.")

    def return_book(self, book, user):
        if book not in self.borrowed_books or user not in self.borrowed_books[book]:
            print("Sorry, you have not borrowed this book.")
            return
        self.books.append(book)
        self.borrowed_books[book].remove(user)
        user.borrowed_books.remove(book)
        print("Book returned successfully.")

    def delete_book(self, book):
        book.is_deleted = True
        print("Book deleted successfully.")

    def get_borrowed_books(self, user):
        borrowed = []
        for book, users in self.borrowed_books.items():
            if user in users:
                borrowed.append(book)
        return borrowed

class User:
    def __init__(self, user_name, user_ID):
        self.user_name = user_name
        self.user_ID = user_ID
        self.borrowed_books = []

在上述代码中，`Book`类中新增了`is_deleted`属性，`Library`类中新增了`delete_book`方法，用于逻辑删除书籍。同时，`borrowed_books`属性使用了字典类型，`get_borrowed_books`方法用于查询某个用户借阅的所有书籍。