Python Day #17: The Complete Beginner’s Guide to Polymorphism in Python

Learn polymorphism in Python with clear examples. Discover how to write cleaner, flexible, and reusable code for any project, from beginner to advanced.

It’s time to keep building on your understanding of OOP and push even further into these concepts, expanding the capabilities of our code.

So far we’ve covered classes and objects, explored Encapsulation as the first pillar of OOP, and last week, we dove into Inheritance — passing down traits from parent classes to child classes so we can write cleaner, more reusable code.

In this lesson, we’re moving on to the third pillar of OOP — one that takes our flexibility in coding to the next level, Polymorphism. What a strange word, try saying it aloud. You might sound a bit crazy when you do for the first time.

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Now the word “Polymorphism” actually originates from Greek. But I’m not here to teach you greek nor do I actually know any greek…

But in code this just refers to the ability of an object or method to take on multiple forms or behaviors depending on the context. Hence the greek meaning of “many forms”

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Recap of Inheritance in OOP

Let’s do a quick recap on the term, Inheritance so we can keep building ont his concept today. A class is rather broad, so many objects can be created and used.

Then we can get more specific with the way we want our programs to act and function so we can define a child class which can have attributes and actions of its own while maintaining the methods inherited from the parent class.

If I ask you, “Do you have a computer?”, That is a yes or no answer. Computer could be seen as the parent class, then we could build out a child class for Windows, Mac, and Linux.

They could inherit many attributes and actions from the parent class but then we could give them their own unique properties and actions as well as they function slightly different.

Now there is something crucial that you want to ask yourself as you begin to build out children to the parent class. Does the child class need new properties (attributes)?

If the answer is yes, then we need to initialize the parent class in the child. If the answer is no, then there is no real need to initialize the parent class.

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Polymorphism in Object-Oriented Programming

You now know a little more about Polymorphism, well just what I touched on but let me tie this into programming now.

Polymorphism lets us to define a method in the parent class and then override it in child classes, each giving it a different behavior.

Why in the world would I want to do this? Well, I’m glad you asked! Because it allows you to write code that’s more flexible, scalable, and easier to maintain.

You can call the same method name without worrying about which exact type of object you’re working with because Python will figure it out at runtime.

Think of it like this: If I tell both a dog and a cat to “speak,” the dog is hopefully going to bark, and the cat might meow. At least I hope that’s what we would hear. The command is the same, but the response depends on the object.

The Third Pillar of OOP in Action

Let me break down polymorphism in its simplest form. I’ll start with a parent class, Animal, that has a method called speak. By default, it doesn’t know what to say — it just sets the structure. This scenario of “Animals” is good for what I want to touch on here in this lesson.

After that I’ll then make two child classes: Dog and Cat. Both will have their own version of speak, one returning "Woof!" and the other "Meow!".

Now, if we loop through a list of animals and call .speak() on each one, Python will execute the correct version for that object without us writing any extra if/else checks.

A different way to think of this is in games. Have you ever played Soul Caliber or Mortal Combat?

Each character has an attack method, but each one behaves differently. With polymorphism, you just call character.attack() and trust that the right behavior will happen.

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Polymorphism in Code

now it’s time to showcase some polymorphism in Python. We will look at two ways to approach this and I’ll touch on how each one works and why it’s useful.

Below in the first block I built out a parent class called Animal. This parent just has one method called speak that returns some English: "This animal makes a sound".

Since you know encapsulation now, we know that this parent class acts as a general template. It’s just a “rough” blueprint to everything else we are doing.

Then below the parent class, I defined two child classes: Dog and Cat. You can see in the parentheses after Dog and Cat I’ve put the parent class, Animal.

This means they both inherit everything from the parent class, but here’s where polymorphism kicks in, both child classes override the speak method to return something different.

Even though the method name is the same in all classes (speak), the behavior changes depending on which object calls it. So when we make objects of Dog and Cat, I can call .speak() on both and each will give its own unique response.

Yes, I know that the code is rather simple, this is just a start. It’s a way to get you introduced to these concepts.

Now we can look at a second path to polymorphism. This is where we often see it become more helpful, it’s when we have multiple objects that share method names, but we don’t even need them to be in the same inheritance chain.

Yeah, that’s right. In Python, polymorphism can work without a strict parent-child relationship, as long as the objects have the same method names.

Imagine this for our next code block: I have two completely separate classes, Car and Boat. Both have a method called move, but each defines it differently.

When I put them into the same loop and call move, Python runs the correct method for each object without me having to check the type.

Here is where things start to move, no pun intended. I don’t care if it’s a Car, Boat, or Plane. I just know it has a move method, and Python handles the rest.

This is great because it means our code can handle new types in the future without having to rewrite everything, which would not be fun in any way, shape or form…

This is really the basics of polymorphism, but gets the gears going. I chose simple class-based examples so you could clearly see the two paths we can take and how they work in practice.

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Wrapping Up Lesson Seventeen

Polymorphism might sound like a big, complicated word, but all it really means is this: you can use the same action, and it will work differently depending on the object you’re using it with.

A dog and a cat can both “speak,” but the dog will bark and the cat will meow. A car and a boat can both “move,” but one drives and the other sails. It’s the same idea, just adapted to the situation.

Once you get the hang of it, you’ll start seeing chances to use this everywhere—not just in parent and child classes, but even in completely separate classes that happen to have the same method name. It’s one of those concepts that, once it clicks, changes the way you think about writing programs.

So the next time you’re building something, look for ways polymorphism can help make your code cleaner, easier to work with, and ready to grow without a lot of rewrites.

Your future self, and anyone else who works on your code, will be glad you did.

Let’s keep moving forward with Day #18 next week.

Hope you all have an amazing week nerds ~ Josh (Chief Nerd Officer 🤓)

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