从主函数 Python 更新类对象

Question

我有一个图书库程序，它的类读取包含@​​987654321@ 和name 的文件并将它们分配给self 对象作为id 和card holder。然后有借书的自我对象，所以我可以识别哪个用户借了哪本书。 问题出在main 函数中，当用户还书时，我不知道如何更新自我借书对象以从对象中删除该书，因此自我id 将没有书借给它。

这是类的外观：

    #loan time length is 3 weeks by default
    LOAN_TIME = 3
    
    class Librarycard:
    
        def __init__(self, card_id, card_holder):
    
    
            self.__id = card_id
            self.__holder = card_holder
    
            #a dictionary that will contain the full book : loan time, updated in later function
            self.__loan = {}
    
        def return_book(self, book):
    
            del self.__loan[book]
            print('returned')
            return

这是我的main功能部分，涉及图书借阅：

    def main():
    
        command = input("Command: ")
        
        #borrowed books main list to check if book borrowed or not
        borrowed_books = []
        
                if command == "R":
        
                    book = input("Book code: ")
        
                    if book not in borrowed_books:
                        print('This book has not been borrowed by anyone')
        
                    else:
                        del borrowed_books[book]
                        print('book returned')
                        
                        # this is where I try to enter the function from the class to update the object 
                        # dictionary 
                        book.return_book(book)
    
    if __name__ == "__main__":
        main()

Answer 1

这里有几个问题。

首先，来自输入的书是一个字符串，而不是实际的书类。所以，当调用book.return_book(book)时，编译器在string类中寻找方法return_book（显然不存在）。

其次，borrowed_books 永远不会在主类中更新，因此用户永远不会归还任何书籍。

第三，不要在 Class 中使用 del，而是使用 self.__loan.pop(book)。它是内置的python函数，是删除书的更好方法。

最后，骆驼案问题很多

这是最终代码可能的样子。

class LibraryCard:
    def __int__ (self, card_id, card_holder):
        self.card_id=card_id
        self.__card_holder=card_holder
        self.checked_out={}
    def return_book (self, book_id):
        popped = self.checked_out.pop(book_id, "Book was already returned, or was never checked out")
        if (popped != "Book was already returned, or was never checked out"): 
            print("Book returned: "+popped)
        else:
            print(popped)
    def isCard(self, id, name):
        return self.card_id==id and self.__card_holder==name


def main():
    cards = {}
    while (true):
        command = input("To check out a book press \"C\", to return a book press \"R\" (without the quotes):\t")
        print("Whether or not you have an account, please follow the instructions below")
            card_id=input("Enter your card id:\t")
        user_name=input("For security purposes, enter your name:\t")
        if (user_id not in cards):
            print("Welcome to Library Services")
            cards[user_id] = LibraryCard(card_id, user_name)
        if (not cards[user_id].isCard(user_id, user_name)):
            print("Wrong user name or user id, please retry")
            continue
        if (command=="C"):
            book=input("Enter the name of the book you would like to check out: ")
            cards[user_id].checked_out[book]=3
            print("Checked out successfully!")
        else:
            book=input("Enter the name of the book you would like to return: ")
            cards[user_id].return_book(book)
            
            
        

 

Answer 2

class Librarycard:

    def __init__(self, card_id, card_holder):
        self.__id = card_id
        self.__holder = card_holder

        # a dictionary that will contain the full book : loan time, updated in later function
        self.__loan = {'tttt': {},"uuuu":{}}

    def return_book(self, book):
        del self.__loan[book]
        print('returned')
        return


def main():
    # command = input("Command: ")
    command = "R"

    # borrowed books main list to check if book borrowed or not
    borrowed_books = ["tttt","aaaa"]

    if command == "R":

        # book = input("Book code: ")
        book = "tttt"
        if book not in borrowed_books:
            print('This book has not been borrowed by anyone')

        else:
            borrowed_books.remove(book)
            print('book returned')

            library_book = Librarycard('card_id', 'you know holder')
            print("before  ",library_book._Librarycard__loan)
            library_book.return_book(book)
            print("after ",library_book._Librarycard__loan)


if __name__ == "__main__":
    main()

C:\Users\sharp\AppData\Local\Programs\Python\Python39\python.exe C:/Users/sharp/Desktop/project/testid.py
book returned
before   {'tttt': {}, 'uuuu': {}}
returned
after  {'uuuu': {}}

Process finished with exit code 0

Answer 3

我已经修复了它，我在主函数中添加了一个连接类的新变量，然后循环运行到类的类键中的所有卡，最后用那个键我激活了退货簿功能。

主要问题是我没有创建要从中删除 book 的 ID 的访问权限。但是一旦使用 for 循环激活，我就能够访问所有 ID'S 对象并从拥有它的那个中删除这本书。

以下是与此问题相关的特定部分的代码：

    def main():
    
        #function that reads the text file and assign the card ids and card holders as a 
        #dictionary.
        library = read_card_data("library.txt")
    
    
         while True:
         command = input("Command: ")
    
            if command == "R":
    
                book = input("Book code: ")
    
                if book not in borrowed_books:
                    print('This book has not been borrowed by anyone')
    
                else:
                    del borrowed_books[book]
    
                    for card in library.keys():
                        library[card].return_book(book)