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Level 0 / Project 05 - Number Classifier

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Before You Start

Recall these prerequisites before diving in: - Can you write an if/elif/else chain that checks multiple conditions? - Do you know what % (modulo) does? What does 10 % 3 return?

Estimated time: 20 minutes

Learn Your Way

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Concept This project — Quiz Flashcards Diagram Browser

Focus

  • if-elif-else decision trees

Why this project exists

Classify numbers as positive/negative/zero, even/odd, and prime/composite. You will build decision trees with if/elif/else and learn the modulo operator for divisibility checks.

Run (copy/paste)

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

cd <repo-root>/projects/level-0/05-number-classifier
python project.py
pytest -q

The program asks for numbers one at a time. Type quit to see a summary.

Expected terminal output

=== Number Classifier ===
Enter numbers one at a time. Type 'quit' to see a summary.

Enter a number (or 'quit'): 7
  7 is positive, odd, prime

Enter a number (or 'quit'): -3
  -3 is negative, odd, composite

Enter a number (or 'quit'): 0
  0 is zero, even, composite

Enter a number (or 'quit'): quit

=== Summary ===
  Numbers classified: 3
  Primes found: 1
  Even numbers: 1
  Odd numbers: 2
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. Add a "perfect number" check (a number equal to the sum of its proper divisors, e.g. 6 = 1+2+3).
  2. After all numbers are entered, ask "Show only primes? (y/n): " and filter the summary.
  3. Re-run script and tests.

Break it (required) — Core

  1. Enter 0 -- is it classified as prime or composite? (It should be neither.)
  2. Enter 1 -- the is_prime() function should return False, but does it?
  3. Enter a negative number like -7 -- does is_prime() handle negatives correctly?

Fix it (required) — Core

  1. Ensure is_prime() returns False for values less than 2.
  2. Add the "neither prime nor composite" label for 0 and 1.
  3. Add a test that verifies is_prime(1) returns False.

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

Explain it (teach-back)

  1. Why does is_prime() only check divisors up to the square root of n?
  2. What is the difference between n % 2 == 0 (even check) and n > 1 and all(...) (prime check)?
  3. Why does classify_number() return a dict instead of printing directly?
  4. Where would number classification appear in real software (data validation, cryptography)?

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.

Stuck? Ask AI

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

  • "I am working on Number Classifier. I got this error: [paste error]. Can you explain what this error means without giving me the fix?"
  • "I am trying to check if a number is prime. I know I need to check divisors, but I am not sure where to stop. Can you give me a hint about the mathematical shortcut?"
  • "Can you explain the modulo operator % with three examples that do not involve prime numbers?"
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