📚 Python Classes and Objects: A Beginner's Guide

 

“Everything in Python is an object.”
Let’s discover how classes and objects work together to build powerful applications!

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🚀 What are Classes and Objects?

Classes are blueprints.
Objects are real-world entities created using these blueprints.

🔵 Diagram:

In Python, everything is an object — integers, strings, lists, even complex numbers!

Example: Complex Numbers as Objects

z = 3 - 5j

Here, z is an instance of the complex class.
Attributes like  and  and methods like  come built-in!

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Differences between Class Diagram and Object Diagram:

Aspect	Class Diagram	Object Diagram
Focus	Shows the design or blueprint of the system	Shows real examples (objects) at a certain time
Representation	Shows classes, their properties, and actions	Shows objects, their values, and their connections
Static vs Dynamic	Static — stays the same while designing	Dynamic — changes depending on what's happening
Usage	Used to plan and design how the system should work	Used to see how things actually look while running

 

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🧱 Defining Your Own Class

Creating a simple empty class:

Now create objects:

Assign attributes dynamically:

Or for s2:

You can even delete attributes:

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🔥 Adding Methods to Classes

Let's make our class more powerful:

Usage:

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🎯 Class Variables vs Object Variables

Aspect	Class Variable	Object Variable
Belongs To	Class itself	Individual Objects
Shared?	Yes	No
Example		name, roll

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🛠️ Special Methods: Magic Behind the Scenes

Python classes have special methods that control behavior:

Method	Purpose
	Constructor
	Pretty print
	Developer representation
	Operator overloading
	Make objects callable

Example:

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🧬 Real-World Example: 3D Vectors

Imagine building a physics engine or 3D model:

Use it like this:

🏗️ Applications: 

3D graphics, simulations, robotics, physics modeling!

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🔒 Public, Protected, and Private Variables

Modifier	Syntax	Access Level
Public		Anywhere
Protected		Within class and subclass
Private		Within class only

🔵 Flowchart:

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🧩 Practice Exercises (With Hints! and solution)

✅ 1. Sphere Class

• Hint:

✅ 2. Account Class

• Hint: Withdraw only if balance ≥ amount!

✅ 3. Rationals Class

• Hint:  methods.

✅ 4. Country Class

• Hint: Calculate density as population/area.

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🎯 Best Practices for Classes in Python

Example for clean class design:

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⭐ Advanced Example: Singleton Class

⚠️ Common Mistakes Beginners Make

Forgetting self in method definitions

Using mutable default arguments

Fix:

Directly accessing private attributes

Instead, use getter/setter methods.

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🛠️ Want More? Advanced OOP Patterns Preview

• 🔥 Factory Pattern: Create objects dynamically without exposing the instantiation logic.
• 🧠 Observer Pattern: Design systems where objects notify others about state changes.

👉 Coming soon in the next blog part! Stay tuned.

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💬 Let’s Connect!

I’d love to hear from you. 🚀

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🔔 Next Challenge Topic Preview:

" Exploring integers with SageMath”