Day 2 – Modules and CLI Utilities

Today's Focus

Structure Python code into functions and modules, and build a small CLI utility that reads and parses real data.

Tasks

• Refactor yesterday's library catalogue code into a proper module structure: catalogue/models.py (data structures), catalogue/filters.py (filter/search logic), catalogue/cli.py (entry point). Use relative imports between them.
• Write a CLI utility using argparse that accepts a CSV file path and one of the subcommands summary, filter, or sort. Each subcommand should have its own arguments (e.g. filter --column genre --value fiction).
• Parse the CSV using the csv module (not pandas). Validate that required columns exist; if not, print a helpful error message and exit with code 1.
• Add a --verbose flag that enables debug-level logging using the logging module. Use logging.DEBUG statements throughout your parsing logic so they appear only when the flag is set.
• Write a __main__.py so your package can be run with python -m catalogue. Test it works from a clean directory.
• Add docstrings (Google or NumPy style) to every function. Run pydoc catalogue.filters to confirm they render correctly.

Reading / Reference

• Python docs: argparse tutorial.
• Python docs: logging HOWTO — the basic and intermediate sections.
• Real Python: Python Modules and Packages.