Python Coding challenge - Day 1274| What is the output of the following Python Code?

 

Explanation:

1. 🏗️ Define the Class

class A:

This creates a class named A.

We will later create an object from this class.

2. 📌 Create a Class Attribute

x = 10

Here, x is a class attribute.

Every object of A can access it unless an instance attribute with the same name overrides it.

So:

a.x

can find the value:

10

3. 🔍 Define __getattr__()

def __getattr__(self, name):

__getattr__() is a special method that Python calls when an attribute cannot be found normally.

The name parameter receives the name of the missing attribute.

For example:

a.y

doesn't find y, so Python effectively calls:

a.__getattr__("y")

4. 🎯 Return a Default Value

return 99

Whenever an attribute is missing, this method returns 99.

So:

a.y

becomes:

99

Notice that __getattr__() does not run for attributes that already exist.

5. 🆕 Create an Object

a = A()

An object a is created from class A.

At this point, a can access the class attribute:

a.x → 10

6. 🖨️ Access a.x

print(a.x, a.y)

First Python evaluates:

a.x

x exists in class A.

Therefore, Python gets:

a.x → 10

__getattr__() is not called.

7. ⚠️ Access a.y

Python then evaluates:

a.y

There is no y attribute in the instance or class.

So Python calls:

__getattr__(a, "y")

The method returns:

99

Therefore:

a.y → 99

🔄 Internal Flow

a.x

 ↓

Found normally

 ↓

10

But:

a.y

 ↓

Not found

 ↓

__getattr__("y")

 ↓

99

🧠 __getattr__() vs __getattribute__()

Method When called?

__getattribute__() For every attribute access

__getattr__() Only when normal lookup fails

💡 Interview Trick

The biggest point to remember:

__getattr__() is a fallback mechanism for missing attributes.

So the final result is:

✅ Output

10 99

Book: 400 Days Python Coding Challenges with Explanation