Python Coding challenge - Day 1072| What is the output of the following Python Code?

 

Code Explanation:

1. Defining Class A

class A:

    data = []

Explanation:

class A: creates a class named A

data = [] defines a class variable named data.

It is an empty list.

Class variables are shared by the class and its subclasses unless overridden.

So initially:

A.data → []

2. Defining Subclass B

class B(A):

    pass

Explanation:

class B(A): means B inherits from class A.

pass means no new attributes or methods are added.

Since B does not define its own data, it inherits data from A.

So:

B.data → refers to A.data

3. Defining Subclass C

class C(A):

    data = []

Explanation:

class C(A): means C also inherits from class A.

But here data = [] creates a new class variable inside C.

This overrides the inherited variable from A.

So now:

A.data → []

B.data → refers to A.data

C.data → []  (separate list)

4. Modifying B.data

B.data.append(1)

Explanation:

B.data refers to A.data because B inherited it.

.append(1) adds 1 to the list.

Since B and A share the same list, the change affects both.

After this operation:

A.data → [1]

B.data → [1]

But:

C.data → []

because C has its own separate list.

5. Printing the Values

print(A.data, B.data, C.data)

Explanation:

A.data → [1]

B.data → [1] (same list as A)

C.data → [] (different list)

6. Final Output

[1] [1] []

Key Concept

Class Variable Inheritance

Class data value Reason

A [1] Original list modified

B [1] Inherited from A

C [] Overridden with its own list

✅ Final Output

[1] [1] []

900 Days Python Coding Challenges with Explanation