Python数据封装与私有属性应用案例

class BankAccount:
    def __init__(self, balance):
        self._balance = balance  # 受保护属性
        self.__secret_code = 1234  # 私有属性

account = BankAccount(1000)
print(account.__secret_code)  # 报错：AttributeError
print(account._BankAccount__secret_code)  # 可以访问，但不推荐

class Temperature:
    def __init__(self, celsius):
        self._celsius = celsius
    @property
    def celsius(self):
        """获取摄氏温度"""
        return self._celsius
    @celsius.setter
    def celsius(self, value):
        """设置摄氏温度，确保不低于绝对零度"""
        if value < -273.15:
            raise ValueError("温度不能低于绝对零度(-273.15℃)")
        self._celsius = value
    @property
    def fahrenheit(self):
        """计算并返回华氏温度"""
        return (self._celsius * 9/5) + 32

temp = Temperature(25)
print(temp.celsius)  # 25
print(temp.fahrenheit)  # 77.0
temp.celsius = -300  # ValueError: 温度不能低于绝对零度(-273.15℃)

class BankAccount:
    def __init__(self, account_holder, initial_balance=0):
        self.account_holder = account_holder
        self._balance = initial_balance
        self.__transaction_history = []
    @property
    def balance(self):
        """获取当前余额"""
        return self._balance
    def deposit(self, amount):
        """存款"""
        if amount <= 0:
            raise ValueError("存款金额必须为正数")
        self._balance += amount
        self.__record_transaction(f"存款: +{amount}")
    def withdraw(self, amount):
        """取款"""
        if amount <= 0:
            raise ValueError("取款金额必须为正数")
        if amount > self._balance:
            raise ValueError("余额不足")
        self._balance -= amount
        self.__record_transaction(f"取款: -{amount}")
    def __record_transaction(self, description):
        """私有方法：记录交易"""
        self.__transaction_history.append(
            f"{datetime.now().isoformat()}: {description}, 余额: {self._balance}"
        )
    def get_statement(self):
        """获取交易记录"""
        return "\n".join(self.__transaction_history)

account = BankAccount("张三", 1000)
account.deposit(500)
account.withdraw(200)
print(account.balance)  # 1300
print(account.get_statement())