demo3_encapsulation.py

"""
demo3: 封装 (Encapsulation)
场景：银行账户——保护余额不被直接修改
"""
from datetime import datetime


class BankAccount:
    bank_name = "招商银行"
    
    def __init__(self, owner: str, initial_balance: float = 0):
        self.owner = owner                    # 公开
        self._balance = initial_balance       # 保护
        self.__pin = "123456"                 # 私有
        self._transactions = []
    
    def deposit(self, amount: float) -> bool:
        if amount <= 0:
            print(f"存款金额必须大于0")
            return False
        self._balance += amount
        self._log("存款", amount)
        print(f"存款成功: +{amount:.2f}, 余额: {self._balance:.2f}")
        return True
    
    def withdraw(self, amount: float) -> bool:
        if amount <= 0:
            print(f"取款金额必须大于0")
            return False
        if amount > self._balance:
            print(f"余额不足! 当前: {self._balance:.2f}")
            return False
        if amount > 5000:
            print(f"单笔取款限额5000")
            return False
        self._balance -= amount
        self._log("取款", amount)
        print(f"取款成功: -{amount:.2f}, 余额: {self._balance:.2f}")
        return True
    
    @property
    def balance(self) -> float:
        return self._balance
    
    def _log(self, type_: str, amount: float):
        self._transactions.append({
            "time": datetime.now().strftime("%H:%M:%S"),
            "type": type_,
            "amount": amount,
            "balance": self._balance
        })
    
    def __validate_pin(self, pin: str) -> bool:
        return pin == self.__pin
    
    def get_statement(self) -> list:
        return self._transactions.copy()
    
    def verify_pin(self, pin: str) -> bool:
        return self.__validate_pin(pin)


if __name__ == "__main__":
    print("=== 封装演示: 银行账户 ===\n")
    account = BankAccount("KeepPush", 1000.0)
    account.deposit(500)
    account.withdraw(200)
    account.withdraw(6000)   # 超限额
    account.withdraw(5000)   # 余额不足
    
    print(f"\n当前余额: {account.balance:.2f}")
    print(f"\n--- 交易明细 ---")
    for t in account.get_statement():
        print(f"  {t['time']} | {t['type']}: {t['amount']:.2f} | 余额: {t['balance']:.2f}")
    
    print(f"\n--- 封装要点 ---")
    print("1. self.owner: 公开属性, 直接访问")
    print("2. self._balance: 保护属性, 通过deposit/withdraw操作")
    print("3. self.__pin: 私有属性, 外部完全不可访问")
    print("4. @property: 只读接口")