Python Coding challenge - Day 1264| What is the output of the following Python Code?

 

Code Explanation:

1️⃣ Creating a Custom Dictionary Class

class D(dict):

Here, D is a custom class that inherits from Python's built-in dict class.

That means objects of D behave like normal dictionaries, but we can add extra behavior.

2️⃣ Defining __missing__()

def __missing__(self, key):

__missing__() is a special dictionary method.

It is automatically called when:

d[key]

tries to access a key that does not exist in the dictionary.

Here, key represents the missing key.

3️⃣ Returning the Missing Key Twice

return key * 2

The missing key is repeated twice.

For example:

key = "b"

then:

"b" * 2

→ "bb"

So the missing key "b" produces "bb".

4️⃣ Creating the Dictionary

d = D(a=10)

A dictionary-like object is created with:

a → 10

So internally:

{"a": 10}

At this point, "b" does not exist.

5️⃣ Accessing the Missing Key

x = d["b"]

Python looks for "b".

It checks:

Is "b" present?

No.

Because D defines __missing__(), Python automatically calls:

__missing__("b")

Then:

"b" * 2

→ "bb"

Therefore:

x = "bb"

6️⃣ Accessing an Existing Key

y = d["a"]

This time "a" already exists:

a → 10

Therefore, __missing__() is not called.

Python directly returns:

10

So:

y = 10

7️⃣ Printing the Result

print(x, y)

We now have:

x = "bb"

y = 10

Therefore the output is:

bb 10

🎯 Final Output

bb 10