Python Coding challenge - Day 921| What is the output of the following Python Code?

 

Code Explanation:

1. Defining a Descriptor Class

class Desc:

A class named Desc is defined.

This class is going to act as a data descriptor.

Data descriptors implement at least one of:

__get__

__set__

__delete__

Here we are defining __set__.

2. Defining __set__ Method

    def __set__(self, obj, val):

        print("SET", val)

This is the critical part:

__set__(self, obj, val) is automatically called when you assign a value to an attribute defined as a descriptor.

Parameters:

self → the descriptor object (Desc instance)

obj → the object whose attribute is being set (a Demo instance)

val → the value being assigned (50)

Instead of storing the value, the method just prints "SET 50"

This is typical in descriptors — they control attribute assignment behavior.

3. Defining a Class That Uses Descriptor

class Demo:

    x = Desc()

A class named Demo is created.

x = Desc() means:

Class attribute x refers to an instance of Desc

Therefore, x becomes a managed attribute

Any assignment to d.x will trigger the descriptor’s __set__

This sets up a binding between Demo.x and Desc.set.

4. Creating an Object of Demo

d = Demo()

d is now an instance of Demo.

It inherits the descriptor attribute x.

At this moment:

Nothing prints yet

No setter is called yet

5. Assigning a Value to d.x

d.x = 50

This is where magic happens:

Because x is a descriptor, Python translates this assignment into:

Desc.__set__(<Desc instance>, d, 50)

Meaning:

The descriptor (Desc() instance) receives:

obj = d

val = 50

So the __set__ method executes:

print("SET", 50)

6. Final Output

SET 50

100 Python Programs for Beginner with explanation