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Level 6 / Project 03 - Idempotency Key Builder

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— This project — — Flashcards — —

Focus

  • stable key generation and dedupe setup

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-6/03-idempotency-key-builder
python project.py --input data/sample_input.txt --output data/output_summary.json
pytest -q

Expected terminal output

{
  "total_input": 6,
  "processed": 4,
  "skipped": 2,
  "stored_keys": 4
}

Expected artifacts

  • data/output_summary.json — dedup results with key counts
  • Passing tests (pytest -q → 7+ passed)
  • Updated notes.md

Alter it (required)

  1. Add a --key-fields CLI argument that lets the user choose which fields form the key (instead of hardcoded source + action).
  2. Add a TTL (time-to-live): keys older than N seconds should be considered expired and allow re-processing.
  3. Add a list_keys CLI subcommand that prints all stored keys with their timestamps.
  4. Re-run script and tests after each change.

Break it (required)

  1. Submit operations with identical source + action but different other fields — observe that they are treated as duplicates.
  2. Change the separator in build_key from | to empty string and create a collision with build_key("ab", "cd") vs build_key("abc", "d").
  3. Pass an input file with missing source or action fields.

Fix it (required)

  1. Add validation that required key fields exist before calling build_key.
  2. Write a test proving the separator prevents accidental collisions.
  3. Handle the "same key, different payload" case by logging a warning.

Explain it (teach-back)

  1. Why is SHA-256 a good choice for idempotency keys vs. a simple string concat?
  2. What does INSERT OR IGNORE do, and how does it differ from INSERT OR REPLACE?
  3. Why is the pipe separator important for avoiding hash collisions?
  4. In what real-world systems would you need idempotency keys?

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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