Python Coding challenge - Day 1125| What is the output of the following Python Code?

 

Code Explanation:

1️⃣ Importing dataclass

from dataclasses import dataclass

Explanation

Imports the dataclass decorator.

It auto-generates methods like __init__, __repr__, etc.

2️⃣ Applying @dataclass

@dataclass

Explanation

Converts class A into a dataclass.

Automatically creates constructor like:

def __init__(self, x=[]):

    self.x = x

⚠️ Important: x=[] is evaluated once, not per object.

3️⃣ Defining Class

class A:

Explanation

Defines class A.

4️⃣ Defining Attribute with Default Value

x: list = []

Explanation ⚠️ CRITICAL

x is given a default value of an empty list.

This list is shared across all instances.

👉 Only ONE list is created in memory.

5️⃣ Creating First Object

a1 = A()

Explanation

a1.x refers to the shared list.

6️⃣ Creating Second Object

a2 = A()

Explanation

a2.x refers to the same shared list.

👉 So:

a1.x is a2.x → True

7️⃣ Modifying List from a1

a1.x.append(1)

Explanation

Adds 1 to the shared list.

👉 Now shared list becomes:

[1]

8️⃣ Printing from a2

print(a2.x)

Explanation

Since a2.x points to the same list:

[1]

📤 Final Output

[1]

Book: 100 Python Projects — From Beginner to Expert