Python Coding challenge - Day 1263| What is the output of the following Python Code?

 

Code Explanation:

1️⃣ Creating the Counter Class

class Counter:

This creates a class named Counter.

The class will maintain a value in self.x and provide special behavior when its object is called like a function.

2️⃣ Defining __init__()

def __init__(self):

__init__() runs automatically when an object of the class is created.

For example:

c = Counter()

causes __init__() to execute.

3️⃣ Initializing x

self.x = 0

The object's x attribute is initialized to 0.

So after:

c = Counter()

we have:

c.x = 0

4️⃣ Defining __call__()

def __call__(self):

__call__() is a special method that allows an object to be called like a function.

Normally:

c

is an object.

But because Counter defines __call__(), we can write:

c()

and Python automatically executes:

c.__call__()

5️⃣ Increasing x

self.x += 2

Every time c() is called, x increases by 2.

Initially:

x = 0

First call:

0 + 2 = 2

Second call:

2 + 2 = 4

Third call:

4 + 2 = 6

6️⃣ Returning the Updated Value

return self.x

After increasing x, the updated value is returned.

So the calls produce:

c() → 2

c() → 4

c() → 6

7️⃣ Creating the Object

c = Counter()

A Counter object is created.

During creation, __init__() sets:

c.x = 0

8️⃣ Calling the Object Three Times

print(c(), c(), c())

This is the tricky part.

Python evaluates the function calls from left to right.

First c()

x = 0

x += 2

x = 2

Returns:

2

Second c()

x = 2

x += 2

x = 4

Returns:

4

Third c()

x = 4

x += 2

x = 6

Returns:

6

Therefore print() receives:

2 4 6

🔄 Complete Execution Flow

Counter()

   ↓

x = 0

   ↓

c()

   ↓

x = 2

   ↓

c()

   ↓

x = 4

   ↓

c()

   ↓

x = 6

🎯 Final Output

2 4 6

Data Structures and Algorithm Design using Python