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Level 4 / Project 12 - Checkpoint Recovery Tool

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Estimated time: 70 minutes

Focus

  • resume from checkpoints safely

Why this project exists

This project gives you level-appropriate practice in a realistic operations context. Goal: run the baseline, alter behavior, break one assumption, recover safely, and explain the fix.

Run (copy/paste)

Use <repo-root> as the folder containing this repository's README.md.

cd <repo-root>/projects/level-4/12-checkpoint-recovery-tool
python project.py --input data/sample_input.txt --output data/processed_output.json --checkpoint data/.checkpoint.json --batch-size 3
pytest -q

Expected terminal output

{
  "total_items": 10,
  "processed": 10,
  "checkpoint_cleared": true
}
6 passed

Expected artifacts

  • data/processed_output.json — processed results
  • data/.checkpoint.json — checkpoint file (cleared on success)
  • Passing tests
  • Updated notes.md

Checkpoint: Baseline code runs and all tests pass. Commit your work before continuing.

Alter it (required) — Extension

  1. Add a --simulate-crash flag that stops after N items to test recovery.
  2. Add a progress bar (percentage) logged at each checkpoint.
  3. Re-run script and tests — verify crash simulation creates a valid checkpoint.

Break it (required) — Core

  1. Corrupt the checkpoint file (write invalid JSON) and run — observe the "starting fresh" behavior.
  2. Modify process_item to raise an exception on a specific item — verify the checkpoint has progress up to the failure point.
  3. Set --batch-size 0 and observe what happens.

Fix it (required) — Core

  1. Validate batch_size is positive in parse_args.
  2. Add error handling in process_item so one bad item does not crash the whole batch.
  3. Re-run until all tests pass.

Checkpoint: All modifications done, tests still pass. Good time to review your changes.

Explain it (teach-back)

  1. Why does save_checkpoint write to a .tmp file first then rename?
  2. What would happen if the process crashed DURING a checkpoint write?
  3. Why is the checkpoint cleared after successful completion?
  4. How would you extend this to support parallel processing with checkpoints?

Mastery check

You can move on when you can: - run baseline without docs, - explain one core function line-by-line, - break and recover in one session, - keep tests passing after your change.

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