Empty list produces a bare IndexError from rotate, rotateRepeat, and printNumbers

[dmccoystephenson]

Current behavior

Rotator.rotate reads inputList[0] (rotator.py:7) before any length check is performed, so an empty list produces a bare IndexError: list index out of range from inside the rotation loop's setup rather than anything that names the caller's mistake. Rotator.rotateRepeat inherits the same behavior for any numRotations >= 1, while rotateRepeat([], 0) returns quietly because range(0) never enters the loop.

Verified against source at 2f70124:

rotate([])            -> RAISES IndexError list index out of range
rotateRepeat([], 0)   -> []
rotateRepeat([], 1)   -> RAISES IndexError list index out of range

main.py's printNumbers is affected by the same class of gap: inputList[numItems - 1] (main.py:9) evaluates to inputList[-1] on an empty list and raises the same bare IndexError.

Why this is worth deciding

The current behavior is now locked in by characterization tests (test_rotate_empty_raises, test_empty_1r_raises, test_printNumbers_empty_raises), so it will not change silently. What has never been decided is whether an empty list should be treated as an error at all — rotating nothing is arguably a well-defined no-op — and, if it is an error, whether the message should say so.

Options

• Treat an empty list as a no-op, returning early from rotate when len(inputList) == 0.
• Keep it an error, but raise with an explanatory message instead of letting a raw index access fail.
• Leave the behavior as-is and consider the characterization tests sufficient documentation.

Whichever option is chosen, the existing characterization tests must be updated in the same change rather than deleted, and the in-place, no-copy constraint stated in README.md must be preserved.

This issue body was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson