Unit Converter CLI

Project roadmap

1. 01

   Set up the argument parser

   ~1h

   Create convert.py and use argparse to accept three optional positional arguments: the value, the source unit and the target unit, plus --list to show supported units and --decimals for rounding. Print the parsed values for now. Done when: python convert.py 5 km mi prints the three values, and --help shows the usage.

2. 02

   Write the conversions

   ~1.5h

   Create dictionaries mapping each length unit to its value in meters and each weight unit to its value in kilograms, and convert by going through the base unit. Temperatures need formulas, so write a function that converts through Celsius for C, F and K. Accept common spellings (km, kilometer and kilometers). Done when: 5 km to mi gives 3.107, and 100 C to F gives 212.

3. 03

   Handle bad input

   ~1h

   Raise and catch clear errors for unknown units (listing similar ones), non-numeric values, mixing categories (kg to m), and temperatures below absolute zero. Print friendly messages and exit with code 1, never showing a traceback. Done when: each kind of bad input prints a helpful message.

4. 04

   Add interactive mode

   ~1h

   When no arguments are given, loop asking for a conversion such as 5 km mi (or a value and units one at a time), print the result, and continue until the user types quit or presses Ctrl+D, handling bad input without leaving the loop. Done when: interactive mode can do several conversions in a row and exits cleanly.

5. 05

   Test and polish

   ~1.5h

   Format results with a sensible number of decimals and unit labels. Write pytest tests for each category, round trips (converting and back gives the original), negative temperatures, unit spellings and every error case. Done when: pytest passes.

Resources

• Docsargparse tutorial
• DocsPython tutorial: dictionaries
• DocsPython tutorial: errors and exceptions
• Docspytest: getting started