Understanding Attributes vs Methods in Python Classes

[Rajeev Bagra]

Why student.exercises_completed Works Without a Method## 🔹 Initial Context

While learning Object-Oriented Programming (OOP) in Python, many beginners encounter code like this:

class Student:
def __init__(self, exercises_completed):
self.exercises_completed = exercises_completed

students = {}
students["Alice"] = Student(12)

print(students["Alice"].exercises_completed)

This works perfectly and prints:

12

But learners often ask:

“I never created a method called exercises_completed.
So how does this line work?”

Let’s understand what is really happening.

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🔹 Step 1: What Happens Inside __init__

Look at this line inside the constructor:

self.exercises_completed = exercises_completed

This line does something very important:

It creates an attribute on the object.

It means:

“Attach a variable named exercises_completed to this object.”

When you write:

Student(12)

Python automatically runs:

self.exercises_completed = 12

So the object now stores this value.

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🔹 Step 2: Attribute vs Method (Key Difference)

In Python, class members are of two main types:

Type	Purpose	Example
Attribute	Stores data	student.exercises_completed
Method	Performs action	student.how_many()

Attribute (Data)

print(student.exercises_completed)

No parentheses → reading stored data.

Method (Function)

print(student.how_many())

Parentheses → calling a function.

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🔹 Step 3: What Is self Really Doing?

Inside the class:

self.exercises_completed = exercises_completed

Means:

• self → the current object
• self.exercises_completed → a variable inside that object

So each Student object gets its own copy.

Example:

a = Student(10)
b = Student(20)

Now:

a.exercises_completed = 10
b.exercises_completed = 20

They are independent.

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🔹 Step 4: How Python Finds Attributes

When you write:

students["Alice"].exercises_completed

Python does:

1️⃣ Get the Student object
2️⃣ Look inside it
3️⃣ Find exercises_completed
4️⃣ Return its value

No method is involved.

---

🔹 Step 5: Seeing Attributes Internally with __dict__

Every object stores its attributes in a dictionary called __dict__.

Try this:

s = Student(15)

print(s.__dict__)

Output:

{'exercises_completed': 15}

This proves that exercises_completed is stored as data.

---

🔹 Step 6: Using a Method Instead (Optional Design)

Sometimes you may want controlled access:

class Student:
def __init__(self, exercises_completed):
self.exercises_completed = exercises_completed

def get_exercises(self):
return self.exercises_completed

Now you use:

print(student.get_exercises())

This is useful when you want validation later.

---

🔹 Step 7: Common Beginner Mistake

Many learners think:

“Dot notation always means method.”

Not true.

Dot notation accesses:

✔ Attributes
✔ Methods
✔ Properties

The difference is parentheses.

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🔹 Step 8: Real-Life Analogy

Think of an object as a student record file.

Inside the file:

Name: Alice
Exercises: 12

You can read “Exercises” directly.

You don’t need a function to see it.

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✅ Final Takeaway

In Python:

Writing self.variable = value inside __init__ creates an attribute.

So:

self.exercises_completed = exercises_completed

Creates:

student.exercises_completed

Which you can access directly.

Remember:

✔ Attributes store data
✔ Methods perform actions
✔ No parentheses → attribute
✔ Parentheses → method

Understanding this difference is essential for mastering object-oriented programming.

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