Lập trình hướng đối tượng trong Python

class BankAccount:
    def __init__(self, balance=0):
        # Double underscores prevent accidental direct access.
        self.__balance = balance

    @property
    def balance(self):
        # Expose read access without exposing mutation.
        return self.__balance

    def deposit(self, amount):
        # Keep validation next to the state it protects.
        if amount <= 0:
            raise ValueError("Amount must be positive")
        self.__balance += amount


account = BankAccount(100)
account.deposit(50)
print(account.balance)  # 150

from abc import ABC, abstractmethod


class PaymentMethod(ABC):
    @abstractmethod
    def pay(self, amount):
        # Callers know what pay does, not how each provider does it.
        pass


class CreditCard(PaymentMethod):
    def pay(self, amount):
        # The concrete class hides its payment implementation.
        return f"Paid ${amount:.2f} by card"


payment = CreditCard()
print(payment.pay(25))

class Employee:
    def __init__(self, name):
        self.name = name

    def describe(self):
        return self.name


class Developer(Employee):
    def __init__(self, name, language):
        # Reuse initialization from the parent class.
        super().__init__(name)
        self.language = language

    def describe(self):
        # Extend inherited behavior instead of duplicating it.
        return f"{super().describe()} writes {self.language}"


print(Developer("Ada", "Python").describe())