Python Coding challenge - Day 1095| What is the output of the following Python Code?

Code Explanation

🔹 1️⃣ Defining Descriptor Class D

class D:

Creates a class D

This class will act as a descriptor

🔹 2️⃣ Defining __get__

def __get__(self, obj, objtype):

    return 100

Called when attribute is accessed

Always returns 100

Parameters:

obj → instance (a)

objtype → class (A)

🔹 3️⃣ Defining __set__

def __set__(self, obj, value):

    obj.__dict__['x'] = value

Called when attribute is assigned

Stores value in instance dictionary

Example:

a.x = 5

would store:

a.__dict__['x'] = 5

🔹 4️⃣ Defining Class A

class A:

Creates class A

🔹 5️⃣ Assigning Descriptor to Class Attribute

x = D()

x is now a descriptor object

Stored in class A

Internally:

A.x → descriptor

🔹 6️⃣ Creating Object

a = A()

Creates instance a

Initially:

a.__dict__ = {}

🔹 7️⃣ Directly Modifying Instance Dictionary

a.__dict__['x'] = 5

Now:

a.__dict__ = {'x': 5}

⚠ Important:

This bypasses __set__

Still creates an instance attribute

🔹 8️⃣ Accessing a.x

print(a.x)

Now Python performs attribute lookup.

🔍 Lookup Order

Python checks in this order:

1️⃣ Data descriptor → ✅ FOUND

2️⃣ Instance dictionary → skipped

3️⃣ Class → skipped

🔹 9️⃣ Descriptor Takes Control

Since x is a data descriptor, Python calls:

D.__get__(descriptor, a, A)

Inside:

return 100

🔹 🔥 Important Observation

Even though:

a.__dict__['x'] = 5

It is ignored because:

👉 Data descriptor has higher priority

Final Output:

100 

Book:  500 Days Python Coding Challenges with Explanation