Why does arr[5:2:-1] return elements in reverse order from index 5 down to 3, but arr[5:2:1] returns an empty array?

hard📝 Conceptual Q10 of 15

NumPy - Indexing and Slicing

Why does arr[5:2:-1] return elements in reverse order from index 5 down to 3, but arr[5:2:1] returns an empty array?

ABecause stop index is inclusive for negative step and exclusive for positive step.

BBecause slicing always returns empty if start > stop.

CBecause positive step requires start < stop; negative step requires start > stop.

DBecause negative step reverses array but positive step does not.

Step-by-Step Solution

Solution:

Step 1: Understand step sign rules
Positive step slices forward and requires start index less than stop index.
Step 2: Negative step slices backward
Negative step slices backward and requires start index greater than stop index.
Final Answer:
Because positive step requires start < stop; negative step requires start > stop. -> Option C
Quick Check:
Step sign controls slice direction and index order [OK]

Quick Trick: Step sign must match start-stop order for valid slice [OK]

Common Mistakes:

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