Python 的面向對象編程（OOP）通過類（Class）和對象（Object）實現代碼結構化，支持封裝、繼承和多態三大特性。以下是系統化指南：

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一、類與對象基礎

1. 定義類

class Dog:# 類屬性（所有實例共享）species = "Canis familiaris"# 構造方法（__init__是魔法方法）def __init__(self, name, age):self.name = name    # 實例屬性self.age = age# 實例方法def bark(self):return f"{self.name} says: Woof!"# 創建對象
my_dog = Dog("Buddy", 3)
print(my_dog.species)  # 輸出: Canis familiaris

2. 特殊方法（Magic Methods）

class Rectangle:def __init__(self, width, height):self.width = widthself.height = height# 計算面積def area(self):return self.width * self.height# 字符串表示（__str__用于用戶友好顯示）def __str__(self):return f"Rectangle({self.width}x{self.height})"# 運算符重載（實現加法）def __add__(self, other):return Rectangle(self.width + other.width,self.height + other.height)rect1 = Rectangle(2, 3)
rect2 = Rectangle(4, 5)
print(rect1 + rect2)  # 輸出: Rectangle(6x8)

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二、繼承與方法重寫

1. 單繼承

class Animal:def __init__(self, name):self.name = namedef speak(self):raise NotImplementedError("子類必須實現此方法")class Dog(Animal):def speak(self):return f"{self.name} says: Woof!"class Cat(Animal):def speak(self):return f"{self.name} says: Meow!"animals = [Dog("Buddy"), Cat("Whiskers")]
for animal in animals:print(animal.speak())

2. 多重繼承

class Flyer:def fly(self):return "Flying!"class Swimmer:def swim(self):return "Swimming!"class Duck(Flyer, Swimmer):def __init__(self, name):self.name = nameduck = Duck("Donald")
print(duck.fly())  # 輸出: Flying!
print(duck.swim()) # 輸出: Swimming!

3. super() 函數

class Rectangle:def __init__(self, width, height):self.width = widthself.height = heightclass ColoredRectangle(Rectangle):def __init__(self, width, height, color):super().__init__(width, height)  # 調用父類構造方法self.color = color

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三、多態與鴨子類型

1. 運行時多態

class Shape:def area(self):passclass Circle(Shape):def __init__(self, radius):self.radius = radiusdef area(self):return 3.14 * self.radius ** 2class Square(Shape):def __init__(self, side):self.side = sidedef area(self):return self.side ** 2def print_area(shape):print(shape.area())print_area(Circle(5))  # 輸出: 78.5
print_area(Square(4))  # 輸出: 16

2. 鴨子類型（Duck Typing）

class Duck:def quack(self):print("Quack!")class FakeDuck:def quack(self):print("Silent quack")def make_quack(duck):duck.quack()make_quack(Duck())       # 輸出: Quack!
make_quack(FakeDuck())   # 輸出: Silent quack

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四、封裝與訪問控制

1. 屬性控制

class BankAccount:def __init__(self, balance=0):self.__balance = balance  # 雙下劃線前綴實現名稱修飾@propertydef balance(self):return self.__balance@balance.setterdef balance(self, value):if value < 0:raise ValueError("余額不能為負")self.__balance = valueaccount = BankAccount(100)
account.balance = 200    # 允許修改
# account.balance = -50  # 拋出 ValueError

2. 描述符協議

class NonNegative:def __set_name__(self, owner, name):self.name = namedef __get__(self, instance, owner):return instance.__dict__[self.name]def __set__(self, instance, value):if value < 0:raise ValueError("值不能為負")instance.__dict__[self.name] = valueclass Product:price = NonNegative()stock = NonNegative()def __init__(self, price, stock):self.price = priceself.stock = stockproduct = Product(19.99, 100)
# product.price = -5  # 拋出 ValueError

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五、高級特性

1. 元類（Metaclass）

class Singleton(type):_instances = {}def __call__(cls, *args, **kwargs):if cls not in cls._instances:cls._instances[cls] = super().__call__(*args, **kwargs)return cls._instances[cls]class Database(metaclass=Singleton):passdb1 = Database()
db2 = Database()
print(db1 is db2)  # 輸出: True

2. 抽象基類（ABC）

from abc import ABC, abstractmethodclass PaymentGateway(ABC):@abstractmethoddef process_payment(self, amount):passclass PayPal(PaymentGateway):def process_payment(self, amount):print(f"PayPal 處理支付: ${amount}")# class FakeGateway(PaymentGateway): pass  # 實例化會報錯

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六、設計模式應用

1. 工廠模式

class ShapeFactory:@staticmethoddef create_shape(shape_type, **kwargs):shapes = {'circle': Circle,'square': Square}return shapes[shape_type](**kwargs)circle = ShapeFactory.create_shape('circle', radius=5)

2. 單例模式

class Database:_instance = Nonedef __new__(cls, *args, **kwargs):if not cls._instance:cls._instance = super().__new__(cls)cls._instance._initialized = Falsereturn cls._instancedef __init__(self):if not self._initialized:self.connect()self._initialized = Truedef connect(self):print("建立數據庫連接")

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七、最佳實踐

1. 組合優于繼承：優先使用對象組合而非類繼承
2. 顯式優于隱式：避免過度依賴魔術方法
3. 保持簡單：單個類職責不超過7個方法（參考SRP原則）
4. 文檔字符串：為每個類和方法編寫docstring
5. 類型注解（Python 3.5+）：

   class Vector:def __init__(self, x: float, y: float):self.x = xself.y = y
   

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掌握這些面向對象技術后，可進一步探索設計模式（如MVC、觀察者模式）和框架開發（如Django的類視圖）。建議通過實際項目（如開發電商系統、游戲引擎）深化理解。