Python Coding challenge - Day 1256| What is the output of the following Python Code?

 

Code Explanation:

1️⃣ Creating an Empty Dictionary

d = {}

An empty dictionary is created.

d → {}

Currently, there is no key named "x".

2️⃣ Using setdefault() for the First Time

a = d.setdefault("x", [])

setdefault() checks whether "x" already exists in d.

Since "x" does not exist, Python:

Creates the empty list []

Stores it as the value of "x"

Returns that same list to a

So:

d → {"x": []}

a → []

Importantly:

a and d["x"] refer to the SAME list.

3️⃣ Adding 10

a.append(10)

Because a and d["x"] point to the same list:

a → [10]

d → {"x": [10]}

No new list is created.

4️⃣ Using setdefault() Again

b = d.setdefault("x", [])

Now "x" already exists.

Therefore, Python does not replace the existing value with a new list.

Instead, it returns the existing list:

b → [10]

d["x"] → [10]

So now:

a is b

is True.

Both variables refer to the same list.

5️⃣ Adding 20

b.append(20)

Since b refers to the same list:

b → [10, 20]

Therefore d["x"] also becomes:

d → {"x": [10, 20]}

6️⃣ Printing the Value

print(d["x"])

The value stored under "x" is:

[10, 20]

✅ Final Output

[10, 20]

200 Days Python Coding Challenges with Explanation