Consider the following Python statement:

num_list = [1, 5, 3, 5, 6, 8, 2, 5, 9, 5]

Which of the following is correct regarding the above statement?

Question

Consider the following Python statement:

num_list = [1, 5, 3, 5, 6, 8, 2, 5, 9, 5]

Which of the following is correct regarding the above statement?

BlackTom AI · Accepted Answer

Python list slicing uses start-inclusive, stop-exclusive semantics and supports negative indices where -1 is the last element.

1. Relevant knowledge points and concepts
- Indexing: num_list = [1,5,3,5,6,8,2,5,9,5] has indices 0..9 for positive indices; negative indices map as -1 -> index 9, -2 -> index 8, etc.
- Slicing semantics: list[a:b] returns elements from index a up to but not including index b. If a or b are negative they are converted to their positive index equivalents. Accessing list[i] returns the single element (not a list).

2. Step-by-step reasoning for each option (showing intermediate steps)
- Map indices: 0:1, 1:5, 2:3, 3:5, 4:6, 5:8, 6:2, 7:5, 8:9, 9:5. Also -1->9, -2->8.
- Option A: num_list[:2] means indices 0 and 1 (since stop=2 exclusive) -> [1, 5]. The option claims [1, 5, 3], so incorrect.
- Option B: num_list[-2:] means start at -2 -> index 8, up to end -> indices 8 and 9 -> [9, 5]. The option claims [5, 9, 5], so incorrect.
- Option C: num_list[2:2] start=2, stop=2 -> no indices included -> [] (empty list). The option claims [3], so incorrect.
- Option D (correct): num_list[-2:-1]. Convert negatives: start=-2 -> index 8, stop=-1 -> index 9. Slicing includes index 8 and excludes index 9, so it returns the element at index 8 only -> [9]. This matches the claim.
- Option E: num_list[3] accesses index 3 directly -> value 5 (not a list). The option claims [3], which is doubly wrong (wrong element and wrong type).

3. Why the correct answer is correct
num_list[-2:-1] maps to start index 8 and stop index 9, and slicing includes index 8 but excludes 9, so the returned sublist contains only the element at index 8, which is 9, producing [9].

4. Why other options are incorrect
Each of A, B, C, E misapply slice boundaries or indexing: A and B list wrong elements and lengths, C misunderstands empty slice when start == stop, and E confuses element access with slicing and gives the wrong value.

Conclusion: The correct option is "num_list[-2:-1] will return [9]", which matches the provided answer.

Consider the following Python statement: num_list = [1, 5, 3, 5, 6, 8, 2, 5, 9, 5] Which of the following is correct regarding the above statement?单项选择题

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