CHAPTER 12 · OOP-BASICS7 min read

Object-oriented programming & classes

As software grows, grouping related data and functions together into Objects becomes essential. A Class acts as a reusable blueprint, while Objects are real instances built from that blueprint.

By the end of this chapter, you can:

Understand classes as blueprints and objects as instances.
Initialize attributes using the __init__() constructor.
Define methods that manipulate object state.

Explanation DepthTailor the level of detail to your learning goal

💻 Standard College Notes

Classes, init constructor, instance attributes, and methods.

A class packages state (attributes) and behavior (methods) together. The __init__(self, ...) method initializes new instances. self represents the specific instance being operated on.

💡Every instance method must take self as its first parameter.

Classes, attributes, and methods in action

The `__init__()` constructor initializes state whenever a new instance is created. `self` refers to the specific instance being operated on.

class CyberBot:
    def __init__(self, name, model):
        self.name = name
        self.model = model
        self.energy = 100

    def recharge(self, amount):
        self.energy = min(100, self.energy + amount)
        print(f"{self.name} recharged! Current energy: {self.energy}%")

bot1 = CyberBot("PodiaBot", "Mark-IV")
print(f"Created {bot1.name} ({bot1.model}) with {bot1.energy}% energy.")
bot1.energy = 45
bot1.recharge(30)

Terminal Output

Ready to execute

Click "▶ Run Code" or press Ctrl+Enter to compile & run this snippet.

✦ Interactive Dry-Run Visualizer

Memory Trace: Object Instantiation & Method Invocation

Follow how RAM instantiates class blueprints into heap objects.

STEP1 / 4

1bot = CyberBot("PodiaBot")👉 Executing

2bot.energy = 45

3bot.recharge(30)

4print(bot.energy)

🧠 RAM / Variable Memory State

Variable	Value in Memory	Data Type
bot.name	"PodiaBot"	auto
bot.energy	100	auto

Instantiate object from CyberBot class

RAM allocates heap memory for the new instance with self.name and self.energy.

Console Stream (stdout)

(No output generated yet)

Line 1: bot = CyberBot("PodiaBot")

🔧 Missing self in Class Method

A class method was defined without self, throwing TypeError when called on an instance.

⚡ +100 XP

fix_bug.pyPython 3.10

⚡ Quick Revision Quiz

Predict The Output (2 Questions)

Question 1 of 2:

What does `self` represent in an instance method?

Question 2 of 2:

What is the initialization method called in Python classes?

Your lightbulb moment

✧

The key takeaway
Object-oriented programming bundles state (attributes) and behavior (methods) into reusable blueprints called classes.

Make it yours

Try creating a second bot instance called bot2 and see how its energy state is completely independent from bot1.

Try editing the code in the playground above in Python, JavaScript, Java, or C++, and use the step-by-step Dry-Run Table to inspect how variables mutate in memory. If you get stuck, click the 🤖 AI Doubt Solver button on your screen for instant explanations!