Skip to content

Level 0 / Project 03 - Temperature Converter

Home: README

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

Before You Start

Recall these prerequisites before diving in: - Can you write a function that takes one argument and returns a calculated result? - Can you use a dictionary to look up a value by key?

Estimated time: 15 minutes

Learn Your Way

Read Build Watch Test Review Visualize Try
Concept This project — Quiz Flashcards Diagram Browser

Focus

  • functions and unit conversion practice

Why this project exists

Convert temperatures between Celsius, Fahrenheit, and Kelvin by routing all conversions through Celsius as a hub. You will learn the hub-and-spoke pattern, which reduces code duplication when supporting multiple unit types.

Run (copy/paste)

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

cd <repo-root>/projects/level-0/03-temperature-converter
python project.py
pytest -q

The program asks for a temperature, source unit, and target unit interactively. Type quit to exit.

Expected terminal output

=== Temperature Converter ===
Supported units: C (Celsius), F (Fahrenheit), K (Kelvin)
Type 'quit' to exit.

Enter temperature value (or 'quit'): 100
Convert from (C/F/K): C
Convert to (C/F/K): F
  100.0 C = 212.0 F

Enter temperature value (or 'quit'): quit
Goodbye!
5 passed

Expected artifacts

  • Passing tests
  • Updated notes.md

Worked Example

Here is a similar (but different) problem, solved step by step.

Problem: Write functions to convert between miles and kilometers, using kilometers as the hub.

Step 1: Write the direct conversion functions.

def miles_to_km(miles):
    return miles * 1.60934

def km_to_miles(km):
    return km / 1.60934

Step 2: Add a hub function that routes conversions. Instead of writing functions for every pair (miles-to-meters, meters-to-miles, etc.), everything goes through km.

def meters_to_km(meters):
    return meters / 1000

def km_to_meters(km):
    return km * 1000

def convert_distance(value, from_unit, to_unit):
    # Step 1: Convert to km (the hub)
    to_km = {"km": lambda v: v, "mi": miles_to_km, "m": meters_to_km}
    # Step 2: Convert from km to target
    from_km = {"km": lambda v: v, "mi": km_to_miles, "m": km_to_meters}

    km_value = to_km[from_unit](value)
    return from_km[to_unit](km_value)

Step 3: Test it. convert_distance(1, "mi", "km") should give 1.60934. convert_distance(1000, "m", "mi") should give about 0.621.

The thought process: The hub-and-spoke pattern means adding a new unit (like feet) only requires two new functions (feet-to-km and km-to-feet), not six new pair functions. This is exactly how the temperature converter works with Celsius as the hub.

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

Alter it (required) — Extension

  1. Add Rankine as a fourth temperature scale (Rankine = Fahrenheit + 459.67).
  2. Ask the user how many decimal places they want in results and round accordingly.
  3. Re-run script and tests.

Break it (required) — Core

  1. Enter -300 as a Kelvin value -- this is below absolute zero. Does convert_temperature() catch it?
  2. Enter X as a unit -- what happens?
  3. Enter hot instead of a number -- does float() fail gracefully?

Fix it (required) — Core

  1. Ensure celsius_to_kelvin() and kelvin_to_celsius() reject temperatures below absolute zero.
  2. Add validation for unknown unit codes in convert_temperature().
  3. Add a test that verifies the below-absolute-zero ValueError.

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

Explain it (teach-back)

  1. Why does the converter route all conversions through Celsius instead of having 6 direct functions?
  2. What is the "hub and spoke" pattern and how does it reduce code duplication?
  3. Why does round() matter for temperature display?
  4. Where would unit conversion code appear in real applications (weather APIs, scientific instruments)?

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 Temperature Converter. I got this error: [paste error]. Can you explain what this error means without giving me the fix?"
  • "I am trying to route all conversions through Celsius as a hub. Can you explain the hub-and-spoke pattern using a different example, like currency conversion?"
  • "Can you explain how to validate that a number is above a minimum value and raise an error if it is not?"
← Prev Home Next →