Python OOP: Inheritance, Polymorphism and Dunder Methods

Python OOP: Inheritance and Dunder Methods

Python's OOP model is elegant and flexible. Dunder methods let your objects integrate seamlessly with Python's built-in features.

class Animal:
    def __init__(self, name, sound):
        self.name  = name
        self.sound = sound

    def speak(self):
        return f"{self.name} says {self.sound}"

    def __repr__(self): return f"Animal({self.name!r})"
    def __str__(self):  return self.name

class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name, 'Woof')
        self.breed = breed

    def speak(self):  # override
        return f"{super().speak()}! (excited)"

animals = [Dog('Rex','Lab'), Animal('Cat','Meow')]
for a in animals: print(a.speak())  # polymorphism

Dunder Methods

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

    def __add__(self, o):   return Vector(self.x+o.x, self.y+o.y)
    def __mul__(self, s):   return Vector(self.x*s, self.y*s)
    def __len__(self):      return 2
    def __getitem__(self, i): return (self.x, self.y)[i]
    def __iter__(self):     yield self.x; yield self.y
    def __eq__(self, o):    return self.x==o.x and self.y==o.y
    def __repr__(self):     return f"Vector({self.x}, {self.y})"

v1 = Vector(1, 2)
print(v1 + Vector(3,4))  # Vector(4, 6)
x, y = v1                 # unpacking via __iter__