Python Coding Challenge - Question with Answer (ID -040226)

 

What is really happening?

Step 1 – Initial list

arr = [1, 2, 3]

The list has three values.

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Step 2 – Loop execution

for i in arr:

Python takes each value one by one and stores it in i.

Iteration	i value	i * 10
1st	1	10
2nd	2	20
3rd	3	30

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Step 3 – The mistake

i = i * 10

Here you are changing only i, not the list.

i is just a copy, not a reference to arr elements.

So:

• arr[0] stays 1

• arr[1] stays 2

• arr[2] stays 3

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Final Result

print(arr)

Output:

[1, 2, 3]

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Memory visualization (easy way)

Think like this:

arr  → [1, 2, 3]
i    → 1 → 10 (dies)
i    → 2 → 20 (dies)
i    → 3 → 30 (dies)

i changes, but arr never changes.

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Correct way to modify the list

Using index:

for i in range(len(arr)):
    arr[i] = arr[i] * 10

Or Pythonic:

arr = [x * 10 for x in arr]

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Interview one-liner:

In Python, loop variables hold values, not references for immutable types like integers.