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Level 2 / Project 04 - Error Safe Divider

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Try in Browser: Run this exercise online — no installation needed!

Before You Start

Recall these prerequisites before diving in: - Can you write a try/except block that catches a specific exception type? - Can you explain the difference between ValueError and TypeError?

Estimated time: 35 minutes

Learn Your Way

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Concept This project — Quiz Flashcards Diagram Browser

Focus

  • exception handling and graceful failure

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-2/04-error-safe-divider
python project.py --input data/sample_input.txt
python project.py --interactive
pytest -q

Expected terminal output

=== Division Results ===
  [OK] 100 / 5 = 20.0
  [FAIL] 10 / 0 = Cannot divide by zero
9 passed

Expected artifacts

  • Division results and summary 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 support for integer division (//) with a --integer flag.
  2. Add a --precision argument to control decimal places in results.
  3. Return results sorted by value (largest first) when --sorted is passed.

Break it (required) — Core

  1. Pass float('inf') as a numerator — what result do you get?
  2. Pass an extremely large number — does Python overflow?
  3. Use a file with no valid operations — does the summary crash?

Fix it (required) — Core

  1. Add a check for float('inf') and float('nan') results.
  2. Handle the empty-results case in summarise_results.
  3. Add tests for infinity and NaN edge cases.

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

Explain it (teach-back)

  1. What is the difference between except ValueError and a bare except?
  2. Why is catching specific exceptions better than catching Exception?
  3. How does try/except/else/finally work — what runs when?
  4. When would error-safe patterns like this be critical in production?

Mastery check

You can move on when you can: - list 5 built-in exception types and when each occurs, - explain exception hierarchy (BaseException vs Exception), - write a try/except that catches multiple specific types, - describe why bare except: is dangerous.

Stuck? Ask AI

If you are stuck after trying for 20 minutes, use one of these prompts:

  • "I am working on Error Safe Divider. I got this error: [paste error]. Can you explain what this error means without giving me the fix?"
  • "I am trying to understand try/except/else/finally. Can you explain what runs in each block with a simple example?"
  • "Can you explain the Python exception hierarchy and why catching Exception is different from catching BaseException?"
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