What is the expected output of the following code? a = [1, 2, 3, 4, 5] print(a[3:0:-1])

Question

Options

• A[4, 3, 2, 1]
• B[4, 3, 2]
• C[4, 3]
• DThe code is erroneous.

• A
  3% (2)
• B
  80% (49)
• C
  11% (7)
• D
  5% (3)

Explanation

Option B is correct because Python's slice a[3:0:-1] starts at index 3 (value 4), steps backward by 1, and stops before reaching index 0 - meaning index 0 (value 1) is excluded. The slice collects indices 3, 2, 1 → values [4, 3, 2].

Why the distractors fail:

• A [4, 3, 2, 1] - This would require a[3::-1] (no stop index), which includes index 0 all the way to the beginning.
• C [4, 3] - This would require a[3:1:-1], stopping before index 1 instead of index 0.
• D - The code is perfectly valid Python; negative steps with slice notation are a core language feature.

Memory tip: The stop index in Python slices is always exclusive - think of it as a fence: you stop at the fence, never stepping on that post. With step=-1, you're walking backwards and stop just before the fence at index 0.

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