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Level 1 / Project 12 - File Extension Counter

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Concept This project — Quiz Flashcards — Browser

Estimated time: 35 minutes

Focus

  • directory scanning and grouped counts

Why this project exists

Count file extensions from a list of paths (or by scanning a directory), then display the distribution with percentages and a bar chart. You will learn Path.suffix, rglob() for recursive scanning, and grouped counting.

Run (copy/paste)

Use <repo-root> as the folder containing this repository's README.md.

cd <repo-root>/projects/level-1/12-file-extension-counter
python project.py --input data/sample_input.txt
pytest -q

Expected terminal output

=== File Extension Counter ===

  .py   5 files (50%)  ##########
  .txt  3 files (30%)  ######
  .md   2 files (20%)  ####

  10 files, 3 unique extensions
4 passed

Expected artifacts

  • data/output.json
  • 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 --filter flag that shows only specific extensions (e.g. --filter .py,.txt).
  2. Add a "hidden files" category for files starting with . (like .gitignore).
  3. Re-run script and tests.

Break it (required) — Core

  1. Point --dir at an empty directory -- does count_extensions() return an empty dict or crash?
  2. Use a file list with files that have double extensions like archive.tar.gz -- which extension is counted?
  3. Point --dir at a path that does not exist -- does it raise NotADirectoryError?

Fix it (required) — Core

  1. Handle the empty-directory case by returning an empty dict with a "(no files found)" message.
  2. Ensure NotADirectoryError is raised with the path in the message for non-existent directories.
  3. Add a test for the empty-directory case.

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

Explain it (teach-back)

  1. Why does count_extensions() use rglob("*") instead of iterdir()?
  2. What does Path.suffix return for a file like archive.tar.gz? (Just .gz -- not .tar.gz.)
  3. Why normalise extensions to lowercase with .lower()?
  4. Where would extension counting appear in real software (disk usage analysis, build systems, file managers)?

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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