Python Coding Challenge - Question with Answer (ID - 031225)

 

✅ Actual Output

[10 20 30]

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Why didn’t the array change?

Even though we write:

i = i + 5

👉 This DOES NOT modify the NumPy array.

 What really happens:

Step	Explanation
for i in x:	i receives a copy of each value, not the original element
i = i + 5	Only changes the local variable i
x	The original NumPy array stays unchanged

So this loop works like:

i = 10 → i = 15 (x unchanged)
i = 20 → i = 25 (x unchanged)
i = 30 → i = 35 (x unchanged)

But x never updates, so output is still:

[10 20 30]

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✅ Correct Way to Modify the NumPy Array

✔ Method 1: Using Index

for idx in range(len(x)):
    x[idx] = x[idx] + 5
print(x)

✅ Output:

[15 25 35]

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✔ Method 2: Best & Fastest Way (Vectorized)

x = x + 5
print(x)

✅ Output:

[15 25 35]

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Key Concept (IMPORTANT for Interviews)

Loop variable in NumPy gives a copy, not a reference.

 To change NumPy arrays, use indexing or vectorized operations.

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