Python Coding Challenge - Question with Answer (ID -111225)

 

Final Output

[1 2 3]

👉 The array does NOT change.

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Why the Array Doesn't Change

🔹 1. for i in a: gives you a copy of each element

• i is just a temporary variable

• It does NOT modify the original array a

So this line:

i = i * 2

✔️ Only changes i
❌ Does NOT change a

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🔹 2. What Actually Happens Internally

Iteration steps:

Loop Step	i Value	i * 2	a (unchanged)
1	1	2	[1 2 3]
2	2	4	[1 2 3]
3	3	6	[1 2 3]

You never assign the new values back into a.

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✅ Correct Way to Modify the NumPy Array

✅ Method 1: Using Index

for i in range(len(a)):
    a[i] = a[i] * 2
print(a)

✅ Output:

[2 4 6]

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✅ Method 2: Vectorized NumPy Way (Best & Fastest)

a = a * 2
print(a)

✅ Output:

[2 4 6]

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Key Concept (Exam + Interview Favorite)

❗ Looping directly over a NumPy array does NOT change the original array unless you assign back using the index.

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