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Level 0 / Project 07 - First File Reader

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Estimated time: 20 minutes

Focus

  • opening and reading plain text safely

Why this project exists

Read a text file, display its contents with line numbers, and build a summary of line counts, word counts, and file metadata. This is your first hands-on practice with file I/O and Path objects.

Run (copy/paste)

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

cd <repo-root>/projects/level-0/07-first-file-reader
python project.py
pytest -q

The program asks you to enter a file path, then displays its contents with line numbers.

Expected terminal output

=== File Reader ===
Enter a file path to read (e.g. data/sample_input.txt): data/sample_input.txt

=== Contents of sample_input.txt ===

  1 | Welcome to your first file reader!
  2 |
  3 | This file has several lines of text.

=== Summary ===
  Lines:      3 (2 non-empty)
  Words:      14
  Characters: 57
5 passed

Expected artifacts

  • Passing tests
  • Updated notes.md

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

Alter it (required) — Extension

  1. Ask the user for a start and end line number to display only a range of the file.
  2. After showing the summary, ask "Read another file? (y/n): " and loop if yes.
  3. Re-run script and tests.

Break it (required) — Core

  1. Enter a file path that does not exist -- does it show a clear error or crash?
  2. Create an empty file and read it -- does file_summary() crash or return zero counts?
  3. Read a file with very long lines (1000+ characters) -- does line numbering still align correctly?

Fix it (required) — Core

  1. Ensure read_file_lines() raises FileNotFoundError with the path in the message.
  2. Handle the empty-file case by returning a special "(empty file)" message.
  3. Add a test for the empty-file edge case.

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

Explain it (teach-back)

  1. Why does format_with_line_numbers() right-justify the line numbers?
  2. What does path.read_text(encoding="utf-8") do differently from open(path).read()?
  3. Why track non-empty lines separately in file_summary()?
  4. Where would file reading with metadata appear in real software (log viewers, code editors, diff tools)?

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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