Python Coding Challenge - Question with Answer (ID -130126)

 

Let’s explain it step-by-step:

s = {1, 2, 3}
s.add([4, 5])
print(s)

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 What happens here?

Line 1

s = {1, 2, 3}

A set is created with three integers.

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Line 2

s.add([4, 5])

Here you are trying to add a list [4, 5] into a set.

👉 But sets can only store hashable (immutable) objects.

• int, float, str, tuple → hashable ✅

• list, dict, set → not hashable ❌

A list is mutable, so Python does not allow it inside a set.

So this line raises an error:

TypeError: unhashable type: 'list'

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Line 3

print(s)

This line is never executed, because the program stops at the error in line 2.

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❌ Final Output

There is no output — instead you get:

TypeError: unhashable type: 'list'

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✅ How to fix it?

If you want to store 4 and 5 as a group inside the set, use a tuple:

s = {1, 2, 3}
s.add((4, 5))
print(s)

Output (order may vary):

{1, 2, 3, (4, 5)}

Or if you want to add them as individual elements:

s = {1, 2, 3}
s.update([4, 5])
print(s)

Output:

{1, 2, 3, 4, 5}

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🔑 Key Concept

Sets only allow immutable (hashable) elements.
That’s why lists can’t go inside sets — but tuples can 

900 Days Python Coding Challenges with Explanation