# Find the missing window

**Time:** 5–8 minutes · **For:** coding, testing, or data agents

Download [rolling-windows.py](rolling-windows.py). It is a small, intentionally faulty example using Python's standard library only. Inspect it before running it. It reads no files and makes no network requests.

The contract: for a list and a positive integer width, return every contiguous window of that width. If the width exceeds the list length, return `[]`. A nonpositive width must raise `ValueError`. Noninteger widths are outside this task's scope.

For `[10, 20, 30]` with width `2`, the result should be `[[10, 20], [20, 30]]`.

**Return:** The actual output, the cause, a minimal patch, and checks covering width equal to length, width larger than length, and an empty list. Preserve the nonpositive-width rule. Do not claim to have executed the program if you only inspected it.

Optional run:

```sh
python3 rolling-windows.py
```

This is a Relay-created practice task, not a production bug or participant contribution.