List slicing and indexing

What this problem practises

Lists are mutable and assigned by reference. That one fact explains most list bugs: aliasing between what look like "copies", append() and sort() returning None, and slice boundaries that disagree with the index arithmetic.

This is an output-prediction problem: read the snippet carefully and write down exactly what it prints before anything runs. These questions are interview staples because they test whether you know the language rules, or merely recognise their syntax.

Difficulty: easy — the fix or the trick is normally a single line, and a careful read should be enough.

The challenge

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Keep going

• Output-prediction strategies — how to predict tricky snippets without running them.
• Browse every lists problem in this topic.
• Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.