Python Coding challenge - Day 1035| What is the output of the following Python Code?

 

Code Explanation:

1. Defining Class A

class A:

    x = "A"

Creates a base class A

Defines a class variable x with value "A"

Any subclass can inherit this variable unless it overrides it

🔹 2. Defining Class B (Inherits from A)

class B(A):

    x = "B"

B inherits from A

x is redefined in B

This overrides A.x for class B and its subclasses

📌 Now:

A.x → "A"

B.x → "B"

🔹 3. Defining Class C (Inherits from A)

class C(A):

    pass

C inherits from A

No x is defined in C

So C uses A.x

📌 C.x → "A"

🔹 4. Defining Class D (Multiple Inheritance)

class D(B, C):

    pass

D inherits from both B and C

No attribute x is defined in D

Python must decide from which parent to take x

➡️ This is where MRO (Method Resolution Order) comes in

🔹 5. Understanding MRO of Class D

Python calculates MRO using the C3 linearization algorithm:

D.mro()

Result:

[D, B, C, A, object]

📌 Meaning:

Python searches attributes in this order:

D

B

C

A

object

🔹 6. Attribute Lookup for D.x

print(D.x)

Step-by-step lookup:

D → ❌ no x

B → ✅ found x = "B"

Stop searching

✅ Final Output

B

400 Days Python Coding Challenges with Explanation