Polymorphism

Polymorphism means “many forms.” In Python, it lets different objects respond to the same method call in their own way.

Think of it like a TV remote’s volume button — it works on any TV brand, but each brand handles the signal differently behind the scenes. You just press the same button and each TV knows what to do.

In Python, polymorphism is mainly achieved through two things: method overriding and duck typing.

Method Overriding

Method overriding is when a subclass has a method with the same name as one in its parent class, but does something different with it.

The way a subclass gets methods from its parent in the first place is called inheritance.

For example, here’s a Shape class with an area() method, and two subclasses — Circle and Rectangle — that each override it to calculate their own area:

class Shape:
    def area(self):
        pass  # 'pass' is a placeholder — this method does nothing on its own
 
class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius
 
    def area(self):
        return 3.14 * self.radius ** 2
 
class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height
 
    def area(self):
        return self.width * self.height

Both Circle and Rectangle have an area() method, but each one calculates area differently. That’s polymorphism in action.

Duck Typing

Duck typing comes from the saying: “If it walks like a duck and quacks like a duck, it’s a duck.”

In Python, this means: if an object has the method you need, you can use it — no matter what class it actually is.

For example, this function works with any object that has an area() method:

def print_area(shape):
    print(f"The area is: {shape.area()}")
 
circle = Circle(5)
rectangle = Rectangle(4, 6)
 
print_area(circle)      # The area is: 78.5
print_area(rectangle)   # The area is: 24

Python doesn’t check what type shape is — it just checks if it has area(). If it does, great. If not, you’ll get an error:

class Triangle(Shape):
    def __init__(self, base, height):
        self.base = base
        self.height = height
 
triangle = Triangle(4, 5)
print_area(triangle)  # AttributeError: Triangle has no area() method

Because Triangle doesn’t define area(), Python can’t call it — even though Triangle inherits from Shape (remember, Shape.area() just has pass, so it doesn’t actually return anything useful).

Try it out