Python Coding Challenge - Question with Answer (ID -060126)

 

Step-by-step Explanation

Line 1

lst = [1, 2, 3]

You create a list:

lst → [1, 2, 3]

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Line 2

lst = lst.append(4)

This is the key tricky part.

• lst.append(4) modifies the list in-place

• But append() returns None

So this line becomes:

lst = None

Because:

lst.append(4) → None

The list is updated internally, but you overwrite lst with None.

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Line 3

print(lst)

Since lst is now None, it prints:

None

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✅ Final Output

None

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 Why this happens

Function	Modifies list	Returns value
append()	Yes	None

So you should not assign it back.

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✅ Correct way to do it

lst = [1, 2, 3]
lst.append(4)
print(lst)

Output:

[1, 2, 3, 4]

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 Summary

• append() changes the list but returns None

• Writing lst = lst.append(4) replaces your list with None

• Always use lst.append(...) without assignment

Book: APPLICATION OF PYTHON FOR CYBERSECURITY