Choose the operation contract, then read why the other choices fail.
Review the related lessons
- Python JSON nonfinite numbers: reject NaN on input and output
- Python heapq priority updates: skip stale entries
- Python topological failure: return a cycle witness
- Python interval capacity sweep: process ends before starts
- Python CSV export: spreadsheet cells are an execution boundary
- Python ipaddress membership: parse the peer before an allowlist
- Python argparse subcommands: require the operation before side effects
Common Mistakes
A browser quiz cannot verify a deployed service or an unfamiliar spreadsheet. Run the linked programs against your own boundary.