多态 #

class Animal:
    def speak(self):
        pass

class Dog(Animal):
    def speak(self):
        return "Woof!"

class Cat(Animal):
    def speak(self):
        return "Meow!"

class Cow(Animal):
    def speak(self):
        return "Moo!"

def animal_sound(animal):
    print(animal.speak())

# 同一函数处理不同类型
animal_sound(Dog())  # "Woof!"
animal_sound(Cat())  # "Meow!"
animal_sound(Cow())  # "Moo!"

class Duck:
    def swim(self):
        print("Duck swimming")
    
    def quack(self):
        print("Quack!")

class Person:
    def swim(self):
        print("Person swimming")
    
    def quack(self):
        print("I'm not a duck!")

def make_it_quack(thing):
    thing.quack()  # 只要能quack就行

make_it_quack(Duck())    # "Quack!"
make_it_quack(Person())  # "I'm not a duck!"

class Shape:
    def area(self):
        raise NotImplementedError

class Rectangle(Shape):
    def __init__(self, w, h):
        self.w = w
        self.h = h
    
    def area(self):
        return self.w * self.h

class Circle(Shape):
    def __init__(self, r):
        self.r = r
    
    def area(self):
        return 3.14 * self.r ** 2

def total_area(shapes):
    return sum(s.area() for s in shapes)

shapes = [Rectangle(2, 3), Circle(5)]
print(total_area(shapes))  # 6 + 78.5

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __add__(self, other):
        return Point(self.x + other.x, self.y + other.y)
    
    def __str__(self):
        return f"({self.x}, {self.y})"

p1 = Point(1, 2)
p2 = Point(3, 4)
p3 = p1 + p2
print(p3)  # "(4, 6)"