Python Coding challenge - Day 1230| What is the output of the following Python Code?

 

Code Explanation:

🔹 1. Importing the weakref Module

import weakref

✅ Explanation

weakref is a built-in Python module.

It allows you to create weak references to objects.

A weak reference does not increase the object's reference count.

If no strong references remain, Python's Garbage Collector automatically deletes the object.

weakref Module

      │

      ▼

Weak References

• WeakValueDictionary

• WeakKeyDictionary

• ref()

• finalize()

Nothing happens yet.

🔹 2. Creating a Class

class A:

    pass

✅ Explanation

A simple empty class named A is created.

pass means the class has no attributes or methods.

It is used only to create an object.

Current Memory

Class A

┌───────────┐

│   Class   │

│     A     │

└───────────┘

No object exists yet.

🔹 3. Creating an Object

obj = A()

✅ Explanation

An object of class A is created.

Current Memory

obj

 │

 ▼

+-------------+

|  Object A   |

+-------------+

Reference Count

Object A

▲

│

obj

Reference Count = 1

There is only one strong reference (obj) pointing to the object.

🔹 4. Creating a WeakValueDictionary

d = weakref.WeakValueDictionary()

✅ Explanation

A WeakValueDictionary is created.

Unlike a normal dictionary:

It stores weak references to values.

It does not own the objects.

If the object disappears, the dictionary removes the entry automatically.

Current Memory

d

{}

Empty Weak Dictionary

🔹 5. Storing the Object

d["x"] = obj

✅ Explanation

The object is stored in the dictionary.

But notice:

The dictionary stores only a weak reference.

It does not increase the reference count.

Current Memory

obj

 │

 ▼

+-------------+

|  Object A   |

+-------------+

      ▲

      │

 Weak Reference

d["x"]

Reference Count

Strong References

obj

Weak References

d["x"]

Still only one strong reference exists.

🔹 6. Deleting the Strong Reference

del obj

✅ Explanation

The variable obj is deleted.

Current Memory Before

obj

 │

 ▼

Object A

After del obj

Object A

No Strong Reference

↓

Garbage Collector Runs

↓

Object Deleted

Since the dictionary contains only a weak reference, it cannot keep the object alive.

Python automatically removes the entry.

Dictionary becomes

{}

🔹 7. Printing Dictionary Keys

print(list(d.keys()))

✅ Explanation

Now the dictionary is empty.

So,

list(d.keys())

returns

[]

Output

[]

🎯 Final Output

[]

Book:

Application of Python in Audio and Video Processing