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Level 3 / Project 11 - Project Config Bootstrap

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— This project — — Flashcards — Browser

Estimated time: 50 minutes

Focus

  • bootstrap config with environment overrides

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-3/11-project-config-bootstrap
python project.py show
python project.py show --config-file config.json
python project.py validate --config-file config.json
python project.py generate default_config.json
pytest -q

Expected terminal output

{"app_name": "myapp", "debug": false, "port": 8000, ...}
Sources:
  app_name: myapp (from default)
  port: 5000 (from file)
12 passed

Expected artifacts

  • Config output on stdout
  • Passing tests
  • Updated notes.md

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

Alter it (required) — Extension

  1. Add support for TOML config files alongside JSON.
  2. Add a --mask-secrets flag that hides secret_key and database_url in output.
  3. Add a diff subcommand that shows which values differ from defaults.

Break it (required) — Core

  1. Set APP_PORT=notanumber as an environment variable — what happens?
  2. Pass a config file with an unknown key — is it ignored or does it crash?
  3. Set port to -1 in the config — does validate catch it?

Fix it (required) — Core

  1. Add type coercion error handling with clear messages.
  2. Warn about unknown config keys instead of ignoring them silently.
  3. Ensure validate_config catches all edge cases (negative values, etc.).

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

Explain it (teach-back)

  1. Why do configs need precedence (defaults < file < env < CLI)?
  2. How does os.environ work and what are environment variables?
  3. What is type coercion and why is it needed for env/CLI string values?
  4. How does monkeypatch.setenv work in pytest?

Mastery check

You can move on when you can: - load configuration from multiple sources with precedence, - coerce string values to typed Python values, - validate configuration for common issues, - test environment variable handling with monkeypatch.

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