Python Coding challenge - Day 977| What is the output of the following Python Code?

 

Code Explanation:

1. Defining the Descriptor Class D

class D:

    def __get__(self, obj, owner):

        obj.__dict__.pop("x", None)

        return 7

Explanation

class D:

Defines a class that will act as a descriptor.

def __get__(self, obj, owner):

This is the descriptor protocol method.

self → the descriptor instance (D()).

obj → the instance accessing the attribute (a).

owner → the class of the instance (A).

obj.__dict__.pop("x", None)

Removes the key "x" from the instance dictionary (a.__dict__) if it exists.

None prevents a KeyError if "x" is not present.

return 7

Always returns the value 7 when the attribute is accessed.

2. Defining the Class A

class A:

    x = D()

Explanation

class A:

Defines a new class.

x = D()

x is a class attribute.

Since D implements __get__, x becomes a non-data descriptor.

Accessing a.x may invoke D.__get__().

3. Creating an Instance of A

a = A()

Explanation

Creates an instance a of class A.

Initially:

a.__dict__ == {}

4. Assigning to a.x

a.x = 3

Explanation

This assignment does not trigger __get__.

Since D does not define __set__, it is a non-data descriptor.

Python allows instance attributes to override non-data descriptors.

Result:

a.__dict__ == {'x': 3}

5. Accessing a.x

print(a.x, a.__dict__)

Step-by-Step Resolution of a.x

Python finds x in a.__dict__ ({'x': 3}).

But since x is also a descriptor in the class:

Python checks the class attribute.

D.__get__(self, obj, owner) is called.

Inside __get__:

"x" is removed from a.__dict__.

7 is returned.

Final State

Value printed for a.x → 7

Instance dictionary becomes:

{}

6. Final Output

7 {}

400 Days Python Coding Challenges with Explanation