Why Object oriented Programming needed#
Functions describe how. Classes describe who.**#
Functions: “Do this action on that data.”
Classes: “This thing knows how to do its own actions.”
Example:
means “Tell some external function to modify this account.”
But
means “The account itself knows how to update its balance.”
The difference is agency — in OOP, data becomes active. This change — from data being passive to data being intelligent — is the essence of why OOP exists.
Classes let you build your own data types.**#
Students already know built-in types:
int, float, list, dict.
Ask:
“What if you could create your own type — like
BankAccountorStudent— that behaves just like built-ins?”
Now:
You just created a new data type — not a function that acts on a dict.
That’s as fundamental as inventing list or set yourself.
It’s not about shorter code — it’s about creating reusable, meaningful data types that model your world.
Classes let your code mirror reality.**#
Without classes:
With classes:
This reads like English. The code is now a story, not a sequence of steps.
You’re no longer “programming instructions.” You’re “building a world” that behaves logically.
That’s what all modern frameworks (like Django, Flask, PyTorch, TensorFlow) do.
Classes let you scale from 10 lines to 10,000.**#
Ask:
“What happens when your system grows?”
In the function version of the shop system:
Every function needs a reference to every piece of data.
Naming conflicts appear.
Adding a new feature means editing 10 functions.
In the class version:
Each class manages itself.
Adding a new feature means editing one class or subclass.
You can reuse the rest untouched.
Scalability isn’t visible in small programs — it’s a design strength.
Classes turn programs into living systems.**#
Imagine your students build a small simulation:
They’ll suddenly see it — each object knows how to act on its own.
You don’t write if type == "dog": print("Woof!") anymore.
You just let the objects behave.
That’s a mental revolution — from control everything manually to let things self-manage.
Classes let teams build together.**#
In real software development:
One person writes a
Shopclass.Another person writes a
Customerclass.Another writes a
Franchiseclass.
Each knows the interface, not the implementation. They don’t step on each other’s toes. That’s how large projects work.
You can’t coordinate teams with only functions and dictionaries — there’s no “ownership” structure.
Classes are the foundation of every major Python framework**#
When students eventually learn:
Pandas → DataFrame class
Scikit-learn → Model class (with
.fit()and.predict())Django → Model and View classes
Matplotlib → Figure and Axes classes
…they’ll see OOP everywhere.
Every powerful tool they use in Python is built with classes.
So the message should be:
“You might not use classes every day, but every professional Python tool you’ll ever use depends on them.”
In short#
Functions make small scripts tidy. Classes make large systems possible.
Functions = steps to perform a task.
Classes = actors that know their roles in the world.
Or as I often tell students:
“When your code needs to remember things, grow, and behave — you stop writing steps, and start creating objects.”
Stage 1 — The “Stupid” Function-Based World#
“Let’s say we want animals that can speak. Simple, right? We’ll just use functions.”
Looks fine… until you add more animals.
Now add 10 more animals#
Now ask:
“What if we also want animals to eat(), sleep(), or move()?” “Will you create a
move(animal_type),eat(animal_type),sleep(animal_type)function with the same long if-elif chain every time?”
It’s clearly ugly, repetitive, and fragile.
If you misspell "dog" somewhere, it silently breaks.
Stage 2 — Enter Classes (and the World Becomes Logical)#
You say:
“Let’s let animals take care of themselves.”
Now, specialized animals inherit from Animal and override only what changes.
Stage 3 — Show the Power (Dynamic Behavior)#
Now all animals share the same interface, and you can treat them uniformly.
Output#
Woof!
The animal moves
The animal eats food
------------------------------
Meow!
The animal moves
The animal eats food
------------------------------
Tweet!
The bird flies
The animal eats food
------------------------------
Hiss!
The snake slithers
The animal eats food
------------------------------
Stage 4 — Add New Animals Instantly#
You now say:
“What if I add an Elephant? Do I need to touch the existing code?”
In the function version, yes — you’d edit a huge if-elif block (and risk breaking others).
In the class version, you simply add a new class.
And it just works:
Output:
Woof!
Meow!
Tweet!
Hiss!
Trumpet!
No if-elif, no touching old code.
That’s inheritance + polymorphism in action.
Stage 5 — Add New Behavior (Extensibility)#
Now, let’s add a new behavior — sleep() — without breaking anything.
All animals inherit it automatically. You didn’t touch the subclasses — they already know how to sleep.
Output:
Zzz...
Zzz...
That’s true scalability — the system grows without breaking.
Stage 6 — Real-World Magic: Collections of Mixed Objects#
Now show the mind-blow moment:
“We can mix all animals in one list and make them all act, without even checking their types.”
Python automatically calls the right method for each animal. This is polymorphism — many forms, one interface.
** Mindset Transformation**#
“In the functions world, you control everything manually — like a puppeteer moving strings. In the class world, you give each puppet a brain — they act on their own.”
That’s why OOP is not about “grouping functions.” It’s about creating intelligent, self-aware entities that manage their own data and actions.
** Bonus: Evolution Example**#
Let’s add another layer of inheritance — subclasses of Bird:
Now:
Output:
Polly wants a cracker!
The bird flies
guess sound?
The eagle soars high in the sky
Woof!
The animal moves
And you can say:
“See — even Birds can have children with different personalities! That’s inheritance working across generations.”
Interactive Pyodide Notebook — Jupyter-Style CodeMirror Version (4 Cells)#
This notebook runs live Python in your browser using Pyodide with real-time syntax highlighting and indentation via CodeMirror.
Features:
Jupyter-like Python highlighting and indentation
Restartable Pyodide kernel
Resizable editors and outputs
Works on mobile (touch-resize + virtual keyboard)
Dark/light theme aware