Python ATM类实例变量self.pin无法匹配验证问题求助

原程序代码 #

class Atm:
    def __init__(self):
        self.pin = ""
        self.balance = 0
        
        
    def menu(self):
            ask = int(input("""

            Select from the menu
            1. Press 1 to set your pin
            2. Press 2 to deposit
            3. Press 3 to withdrawl
            4. Press 4 to check balance
            5. Press 5 to exit
        
            :  """))
            if ask == 1:
                self.create_pin()
            elif ask == 2:
                self.deposit()
            
    def create_pin(self):
        self.pin = input(" Set your pin : ")
        print(" Pin sucesfully set ")
    
    
    def deposit(self):
        print(self.pin)
        tmp = input(" Enter your pin : ")
        if tmp == self.pin:
            amount = float(input(" Enter your deposit amount  : "))
            self.balance = amount + self.balance
            print(" Amount Deposit sucessfully ")
        else:
            print(" Wrong Pin ")
            
                        
        


sbi = Atm()
sbi.menu()

问题描述 #

编写上述ATM程序后，通过create_pin方法设置PIN后，在deposit方法验证时始终进入else分支，输出“Wrong Pin”。

复现步骤 #

• 运行程序
• 选择1设置PIN为1234
• 重新运行程序
• 选择2存款并输入PIN 1234，输出“Wrong Pin”

期望效果 #

输入的临时变量tmp与预设PIN匹配时，允许用户存款。

问题根源 #

不是deposit方法逻辑错误，而是程序内存生命周期问题：
每次运行程序都会重新创建Atm类实例sbi，上一次运行时设置的PIN仅存在于当时的内存中，程序结束后内存释放，数据丢失。第二次运行时self.pin回到初始空字符串""，输入的1234与空字符串不匹配，因此触发错误提示。

解决方案 #

方案1：单次运行内完成所有操作（无需持久化） #

当前菜单仅处理一次用户选择就结束，修改为循环结构，让用户在一次运行中完成PIN设置、存款等操作，无需重启程序：

class Atm:
    def __init__(self):
        self.pin = ""
        self.balance = 0
        
    def menu(self):
        while True:  # 加入循环，持续显示菜单
            ask = int(input("""

            Select from the menu
            1. Press 1 to set your pin
            2. Press 2 to deposit
            3. Press 3 to withdrawl
            4. Press 4 to check balance
            5. Press 5 to exit
        
            :  """))
            if ask == 1:
                self.create_pin()
            elif ask == 2:
                self.deposit()
            elif ask == 3:
                self.withdraw()
            elif ask == 4:
                self.check_balance()
            elif ask == 5:
                print("退出程序")
                break
            else:
                print("无效选项，请重新选择")
            
    def create_pin(self):
        self.pin = input("Set your pin: ").strip()  # 去除输入前后空格
        print("Pin successfully set")
    
    def deposit(self):
        if not self.pin:
            print("请先设置PIN")
            return
        tmp = input("Enter your pin: ").strip()
        if tmp == self.pin:
            amount = float(input("Enter your deposit amount: "))
            self.balance += amount
            print("Amount deposited successfully")
        else:
            print("Wrong Pin")
            
    def withdraw(self):
        if not self.pin:
            print("请先设置PIN")
            return
        tmp = input("Enter your pin: ").strip()
        if tmp == self.pin:
            amount = float(input("Enter your withdrawal amount: "))
            if amount <= self.balance:
                self.balance -= amount
                print("Amount withdrawn successfully")
            else:
                print("余额不足")
        else:
            print("Wrong Pin")
            
    def check_balance(self):
        if not self.pin:
            print("请先设置PIN")
            return
        tmp = input("Enter your pin: ").strip()
        if tmp == self.pin:
            print(f"当前余额: {self.balance:.2f}")
        else:
            print("Wrong Pin")
            
sbi = Atm()
sbi.menu()

修改说明：

• 菜单加入while True循环，支持多次操作直到选择退出
• 输入时用.strip()去除前后空格，避免误输入空格导致匹配失败
• 补充取款、余额查询功能，操作前先检查是否已设置PIN

方案2：持久化PIN和余额（重启程序后数据保留） #

如果需要重启程序后仍保留数据，可通过JSON文件存储PIN和余额：

import json
import os

class Atm:
    def __init__(self):
        self.data_file = "atm_data.json"
        self.load_data()  # 初始化时加载保存的数据
        
    def load_data(self):
        if os.path.exists(self.data_file):
            with open(self.data_file, "r") as f:
                data = json.load(f)
                self.pin = data.get("pin", "")
                self.balance = data.get("balance", 0.0)
        else:
            self.pin = ""
            self.balance = 0.0
            
    def save_data(self):
        data = {"pin": self.pin, "balance": self.balance}
        with open(self.data_file, "w") as f:
            json.dump(data, f)
        
    def menu(self):
        while True:
            ask = int(input("""

            Select from the menu
            1. Press 1 to set your pin
            2. Press 2 to deposit
            3. Press 3 to withdrawl
            4. Press 4 to check balance
            5. Press 5 to exit
        
            :  """))
            if ask == 1:
                self.create_pin()
            elif ask == 2:
                self.deposit()
            elif ask == 3:
                self.withdraw()
            elif ask == 4:
                self.check_balance()
            elif ask == 5:
                print("退出程序")
                break
            else:
                print("无效选项，请重新选择")
            
    def create_pin(self):
        self.pin = input("Set your pin: ").strip()
        self.save_data()  # 设置PIN后保存数据
        print("Pin successfully set")
    
    def deposit(self):
        if not self.pin:
            print("请先设置PIN")
            return
        tmp = input("Enter your pin: ").strip()
        if tmp == self.pin:
            amount = float(input("Enter your deposit amount: "))
            self.balance += amount
            self.save_data()  # 修改余额后保存数据
            print("Amount deposited successfully")
        else:
            print("Wrong Pin")
            
    def withdraw(self):
        if not self.pin:
            print("请先设置PIN")
            return
        tmp = input("Enter your pin: ").strip()
        if tmp == self.pin:
            amount = float(input("Enter your withdrawal amount: "))
            if amount <= self.balance:
                self.balance -= amount
                self.save_data()  # 修改余额后保存数据
                print("Amount withdrawn successfully")
            else:
                print("余额不足")
        else:
            print("Wrong Pin")
            
    def check_balance(self):
        if not self.pin:
            print("请先设置PIN")
            return
        tmp = input("Enter your pin: ").strip()
        if tmp == self.pin:
            print(f"当前余额: {self.balance:.2f}")
        else:
            print("Wrong Pin")
            
sbi = Atm()
sbi.menu()

修改说明：

• 加入JSON文件读写逻辑，实现数据持久化
• 每次修改PIN或余额后调用save_data()保存到文件
• 程序启动时自动加载之前保存的数据，重启后仍可使用原有PIN和余额

内容的提问来源于stack exchange，提问作者Rishabh Shrivasatava