Polymorphism

# Duck typing — if it walks like a duck...
class Duck:
    def speak(self): return "Quack!"
    def swim(self): return "Swimming..."

class Person:
    def speak(self): return "Hello!"
    def swim(self): return "Doing the backstroke..."

# Both have speak() and swim() — polymorphism!
def interact(entity):
    print(entity.speak())
    print(entity.swim())

interact(Duck())
interact(Person())

# Operator overloading
class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y)
    
    def __repr__(self):
        return f"Vector({self.x}, {self.y})"
    
    def __len__(self):
        return int((self.x**2 + self.y**2) ** 0.5)

v1 = Vector(3, 4)
v2 = Vector(1, 2)
v3 = v1 + v2
print(f"{v1} + {v2} = {v3}")
print(f"Length of {v1}: {len(v1)}")