Python Coding challenge - Day 967| What is the output of the following Python Code?

 

Code Explanation:

1. Defining a Custom Metaclass

class AutoID(type):

AutoID is a metaclass because it inherits from type.

A metaclass controls how classes are created.

2. Defining a Class-Level Counter

    counter = 0

counter is a class variable of the metaclass.

It is shared across all classes created using AutoID.

3. Overriding the Metaclass __new__ Method

    def __new__(cls, name, bases, dct):

        dct["id"] = cls.counter

        cls.counter += 1

        return super().__new__(cls, name, bases, dct)

__new__ is called whenever a class using this metaclass is created.

Parameters:

cls → the metaclass (AutoID)

name → name of the class being created

bases → base classes

dct → class attributes

What it does:

Inserts an attribute id into the class dictionary with the current counter value.

Increments the counter for the next class.

Creates the class normally.

4. Creating Class A

class A(metaclass=AutoID): pass

Triggers AutoID.__new__(..., "A", ...)

counter is 0, so:

A.id = 0

Then counter becomes 1.

5. Creating Class B

class B(metaclass=AutoID): pass

Triggers AutoID.__new__(..., "B", ...)

counter is now 1, so:

B.id = 1

Then counter becomes 2.

6. Printing the IDs

print(A.id, B.id)

Prints the class attributes id of A and B.

7. Final Output

0 1

400 Days Python Coding Challenges with Explanation