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Level 3 / Project 12 - Parser With Fixtures

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— This project — — Flashcards — Browser

Estimated time: 55 minutes

Focus

  • test fixtures and parser stability

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-3/12-parser-with-fixtures
python project.py data/sample_input.txt
python project.py data/sample_input.txt --format ini --json
pytest -q

Expected terminal output

Format: ini, Lines: 15
[database]
  host = localhost
  port = 5432
...
18 passed

Expected artifacts

  • Parsed output on stdout
  • Passing tests with fixture-generated files
  • Updated notes.md

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

Alter it (required) — Extension

  1. Add a YAML-like parser (indentation-based key: value pairs).
  2. Add --validate flag that checks all sections have at least one entry.
  3. Add line number tracking to each parsed record for error reporting.

Break it (required) — Core

  1. Parse an INI file with duplicate section names — what happens?
  2. Parse a CSV with quoted fields containing commas — does simple split work?
  3. Auto-detect format on ambiguous input (e.g., a=b,c=d) — which parser wins?

Fix it (required) — Core

  1. Handle duplicate sections by merging entries (or warning).
  2. Document that the CSV parser doesn't handle quoted fields (limitation).
  3. Add a --format override so users can bypass auto-detection.

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

Explain it (teach-back)

  1. What is a pytest fixture and how does it differ from setup/teardown?
  2. Why do the fixtures use tmp_path instead of real files?
  3. How does detect_format use heuristics to guess the file type?
  4. What is the registry pattern (PARSERS dict) and why use it?

Mastery check

You can move on when you can: - write pytest fixtures that create temporary test data, - build parsers for multiple text formats, - use a registry pattern to dispatch to the right parser, - auto-detect file formats from content.

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