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Level 3 / Project 09 - Reusable Utils Library

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— This project — — Flashcards — Browser

Estimated time: 45 minutes

Focus

  • common helper functions and reuse

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-3/09-reusable-utils-library
python project.py slugify "Hello World!"
python project.py convert my_variable_name --to camel
python project.py validate user@example.com --type email
pytest -q

Expected terminal output

hello-world
myVariableName
{"valid": true, ...}
18 passed

Expected artifacts

  • Utility outputs 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 deep_flatten function that flattens arbitrarily nested lists.
  2. Add a validate_phone function similar to validate_email.
  3. Add a pluralize string utility (simple English rules: "cat" -> "cats").

Break it (required) — Core

  1. Call chunk with size 0 — what happens?
  2. Call slugify with only special characters — what is returned?
  3. Call camel_to_snake on an already-snake string — is the result correct?

Fix it (required) — Core

  1. Ensure chunk raises a clear error for non-positive sizes.
  2. Handle edge case where slugify produces an empty string.
  3. Add idempotency: camel_to_snake(snake_to_camel(x)) should round-trip.

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

Explain it (teach-back)

  1. What makes a function "reusable" vs. tightly coupled to one project?
  2. Why write docstrings with input/output examples?
  3. How does re.sub work for text transformation?
  4. Why use set() in unique_ordered for O(1) membership checking?

Mastery check

You can move on when you can: - design small, composable utility functions, - write clear docstrings with examples, - test edge cases and boundary conditions, - use regex for text transformation.

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