``python def func(item): item += [1] data = [1, 2, 3, 4] func(data) print(len(data)) `` What is the expected output of the following code?

Question

def func(item):
 item += [1]

data = [1, 2, 3, 4]
func(data)
print(len(data))

Options

• A5
• B4
• C2
• DThe code is erroneous.

• A
  75% (27)
• B
  14% (5)
• C
  8% (3)
• D
  3% (1)

Explanation

Option A is correct because += on a Python list performs in-place mutation via __iadd__, which is equivalent to calling item.extend([1]). This modifies the original list object that data points to, appending 1 to it - so data becomes [1, 2, 3, 4, 1] with length 5.

B (4) is wrong because it assumes += rebinds the local variable like item = item + [1] would - but for lists, += mutates the existing object rather than creating a new one, so the change is visible outside the function. C (2) has no logical basis in this code. D is wrong because the code is syntactically and semantically valid; it runs cleanly with no exceptions.

Memory tip: Think of list += other as "extend in place" (changes the original) vs. list = list + other as "create a new list" (original unchanged). When in doubt, ask: does += call extend or =? For lists, it always calls extend.

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