Python Coding Challenge - Question with Answer (ID -081225)

 

Step 1: Initial List

clcoding = [1, 2, 3]

List length = 3

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 Step 2: Understanding the Lambda

f = lambda x: (clcoding.append(0), len(clcoding))[1]

This line does two things at once using a tuple:

Part	What it Does
clcoding.append(0)	Adds 0 to the list
len(clcoding)	Gets updated length
[1]	Returns second value only

✅ So each time f(x) runs → list grows by 1 → new length is returned

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 Step 3: map() is Lazy

m = map(f, clcoding)

 map() does NOT run immediately.
It runs only when next(m) is called.

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 Step 4: Execution Loop (3 Times)

▶ First next(m)

• List before: [1, 2, 3]

• append(0) → [1, 2, 3, 0]

• len() → 4

• ✅ Prints: 4

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▶ Second next(m)

• List before: [1, 2, 3, 0]

• append(0) → [1, 2, 3, 0, 0]

• len() → 5

• ✅ Prints: 5

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▶ Third next(m)

• List before: [1, 2, 3, 0, 0]

• append(0) → [1, 2, 3, 0, 0, 0]

• len() → 6

• ✅ Prints: 6

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 Final Output

4
5
6

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Key Concepts Used (Interview Important)

• ✅ map() is lazy

• ✅ Mutable list modified during iteration

• ✅ Tuple execution trick inside lambda

• ✅ Side-effects inside functional calls

800 Days Python Coding Challenges with Explanation