Python Coding challenge - Day 1143| What is the output of the following Python Code?

 

Code Explanation:

🔹 1. Class Definition

class Test:

✅ Explanation:

A class Test is created.

It will store a list in each object.

🔹 2. Constructor (__init__)

def __init__(self, x=[]):

    self.x = x

✅ Explanation:

Constructor runs when object is created.

Parameter x=[] is a default argument.

⚠️ Important:

This list is created only once

It is shared across all objects

🔹 3. Assigning to Instance

self.x = x

✅ Explanation:

Assigns the same list (x) to the object

Since x is shared → all objects refer to same list

🔹 4. Creating First Object

a = Test()

✅ What happens:

No argument passed → uses default list []

So:

a.x → []

🔹 5. Creating Second Object

b = Test()

✅ What happens:

Again uses SAME default list

So:

b.x → []

⚠️ Key Insight:

a.x is b.x → True

👉 Both refer to same list

🔹 6. Modifying List via a

a.x.append(1)

✅ Explanation:

Adds 1 to the shared list

So now:

a.x → [1]

b.x → [1]

🔹 7. Printing b.x

print(b.x)

✅ Output:

[1]

Final Output:

[1]

Book:  700 Days Python Coding Challenges with Explanation