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Level 2 / Project 09 - Config Driven Calculator

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Concept This project — Quiz Flashcards Diagram Browser

Estimated time: 40 minutes

Focus

  • read behavior from json config

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-2/09-config-driven-calculator
python project.py --config data/sample_input.txt --list
python project.py --config data/sample_input.txt --op add --a 10 --b 5
python project.py --config data/sample_input.txt --op divide --a 10 --b 0
pytest -q

Expected terminal output

{"success": true, "operation": "add", "a": 10.0, "b": 5.0, "result": 15.0}
10 passed

Expected artifacts

  • Calculation results 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 a sqrt operation that only uses the --a operand.
  2. Add a --chain mode: --chain "add:5,multiply:2" starting from --a.
  3. Use settings.precision from the config to control decimal places.

Break it (required) — Core

  1. Pass a config file with missing "operations" key.
  2. Compute 2 ** 1000 — does the result overflow?
  3. Pass non-numeric values for --a or --b.

Fix it (required) — Core

  1. Add config.setdefault for missing keys.
  2. Check for overflow/infinity in calculate results.
  3. Wrap float() conversion in try/except in batch mode.

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

Explain it (teach-back)

  1. Why is config-driven design useful vs hard-coding operations?
  2. How does dict.setdefault differ from dict.get?
  3. What is the Strategy pattern and how does this project resemble it?
  4. When would you use JSON config files in real applications?

Mastery check

You can move on when you can: - load and validate JSON config from memory, - add a new operation by editing only the config file, - explain the difference between hard-coded and config-driven behaviour, - implement operation chaining from scratch.

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