Day 4 – Virtual Envs and Dependencies

Today's Focus

Set up a professional Python project with virtual environments, dependency management, and a reproducible install.

Tasks

• Create a fresh project directory and set up a virtual environment three ways: python -m venv .venv, then pipenv install, then poetry init. Compare the resulting files (requirements.txt vs Pipfile vs pyproject.toml). Pick one approach and stick with it for the rest of the week.
• Using your chosen tool, add pytest, ruff, and black as dev dependencies and your project's runtime dependencies separately. Confirm they appear in the correct dependency groups.
• Pin all dependencies to exact versions: pip freeze > requirements.txt (for venv) or equivalent. Explain in a comment why pinning matters for reproducibility in CI.
• Write a pyproject.toml that defines your project metadata (name, version, description, requires-python) alongside [tool.ruff] and [tool.black] config sections.
• Create a Makefile with targets: make install (set up venv and install deps), make test (run pytest), make lint (run ruff and black --check), make format (run black). Test each target from scratch in a new shell.
• Delete your virtual environment, run make install, and confirm all tests still pass — this validates your lockfile / pinned deps.

Reading / Reference

• Python Packaging User Guide — the "Managing Application Dependencies" tutorial.
• Poetry documentation — Dependency specification and Dependency groups.
• Ruff documentation — Rules reference and pyproject.toml configuration.