Python Coding Challenge - Question with Answer (ID -301125)

 

What is happening?

🔹 1. map() creates an iterator

res = map(lambda x: x + 1, nums)

This does NOT create a list immediately. It creates a lazy iterator:

res → (2, 3, 4)

…but nothing is calculated yet.

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🔹 2. The for loop consumes the iterator

for i in res: 
    pass

• This loop runs through all values: 2, 3, 4

• But since we used pass, nothing is printed

• Important: After this loop, the iterator is now EXHAUSTED

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🔹 3. Printing after exhaustion

print(list(res))

• res is already empty

• So converting it to a list gives:

[]

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✅ Final Output

[]

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Key Tricky Rule

 A map() object can be used ONLY ONCE.
Once it is looped through, it becomes empty forever.

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✅ Correct Way (If you want reuse)

res = list(map(lambda x: x + 1, nums))

for i in res:
    pass
print(res) # [2, 3, 4]

Python for Civil Engineering: Concepts, Computation & Real-world Applications