Python Coding challenge - Day 1207| What is the output of the following Python Code?

 

Code Explanation:

🔹 1. Creating an Empty Dictionary

data = {}

✅ Explanation

An empty dictionary named data is created.

It currently contains no keys and no values.

Current memory:

data

↓

{}

🔹 2. Calling setdefault()

data.setdefault("x", [])

✅ Explanation

The syntax of setdefault() is:

dictionary.setdefault(key, default_value)

It works like this:

If the key already exists, return its value.

If the key does not exist, create it using the default value and return that value.

Here,

Key → "x"

Default Value → [] (an empty list)

Python checks:

Does "x" exist?

↓

No ❌

So Python creates the key.

Current dictionary:

{

   "x": []

}

🔹 3. Appending the First Value

data.setdefault("x", []).append(10)

✅ Explanation

After setdefault() returns the list, Python immediately calls:

.append(10)

Internally, it behaves like:

data["x"].append(10)

Before appending:

"x"

↓

[]

After appending:

"x"

↓

[10]

Current dictionary:

{

   "x":[10]

}

🔹 4. Calling setdefault() Again

data.setdefault("x", [])

✅ Explanation

Python again checks:

Does "x" exist?

↓

Yes ✅

Since the key already exists,

Python does not create a new list.

Instead, it simply returns the existing list.

Current dictionary remains:

{

   "x":[10]

}

🔹 5. Appending the Second Value

.append(20)

✅ Explanation

Now Python appends 20 to the same list.

Before:

[10]

After:

[10,20]

Current dictionary:

{

   "x":[10,20]

}

🔹 6. Printing the Dictionary

print(data)

✅ Explanation

Python prints the final dictionary.

Output:

{'x': [10, 20]}

🎯 Final Output

{'x': [10, 20]}

Book:  700 Days Python Coding Challenges with Explanation