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Level 7 / Project 09 - Contract Version Checker

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Focus

  • payload version compatibility checks

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-7/09-contract-version-checker
python project.py --input data/sample_input.txt --output data/output_summary.json
pytest -q

Expected terminal output

... output_summary.json written ...
2 passed

Expected artifacts

  • data/output_summary.json
  • Passing tests
  • Updated notes.md

Alter it (required)

  1. Add a "nullable" attribute to ContractField so a field can be present but None.
  2. Add a backwards_compatible() function that checks if new contract is safe to deploy.
  3. Re-run script and tests — verify nullable fields and compatibility check work.

Break it (required)

  1. Pass a version string with only two parts (e.g. "2.1") and watch parse_version crash.
  2. Send a payload where a required field is present but set to None.
  3. Observe the IndexError or false-positive validation pass.

Fix it (required)

  1. Pad missing version parts with zero (e.g. "2.1" becomes "2.1.0").
  2. Treat None values as missing for required fields in validate_payload.
  3. Add tests for two-part versions and None-valued required fields.

Explain it (teach-back)

  1. Why is semantic versioning important for API contracts?
  2. What happened when the version string had only two parts?
  3. How did the padding fix prevent the IndexError?
  4. How do real API platforms handle breaking vs non-breaking changes?

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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