Day 25 of 30: 📦 Packaging & Distribution

Turn your code into an installable package, build wheels, and (optionally) publish it — step by step.

May 25, 2025

🔄 Quick Recap (Day 24)

You wrote tests with unittest/pytest and learned how to debug with breakpoints and tracebacks.

🎯 What You’ll Learn Today

A simple project structure for a Python package.
How to configure pyproject.toml with setuptools.
How to build sdist (source) and wheel (binary) files.
How to install your package locally and add a CLI command.
How to (optionally) publish to TestPyPI with twine.
Friendly versioning and metadata tips.

📖 Why Package Your Code?

Packaging lets anyone (including you on another computer) install your project with one command: pip install yourpackage. It’s useful for:

Reusing utilities across projects.
Sharing tools with classmates or teammates.
Creating small command‑line apps you can run from any folder.

Two build types:
• sdist = a source archive of your code.
• wheel = a ready‑to‑install build (faster to install).

📖 Project Layout

Create a new folder, e.g. dmagogreet/, with this structure:

dmagogreet/
├─ dmagogreet/
│  ├─ __init__.py
│  └─ cli.py
├─ pyproject.toml
├─ README.md
└─ LICENSE   (optional)

What each file does:

dmagogreet/: your actual Python package (same name as the project).
__init__.py: makes it a package; good place for __version__.
cli.py: code for a tiny command‑line tool.
pyproject.toml: build configuration (who you are, version, entry points).
README.md: a short “what it does / how to use it.”

`dmagogreet/init.py`

__version__ = "0.1.0"

def greet(name: str) -> str:
    return f"Hello from Digital Mago, {name}!"

`dmagogreet/cli.py`

from . import greet, __version__


def main() -> None:
    import argparse
    p = argparse.ArgumentParser(description="Digital Mago greeter")
    p.add_argument("name", help="Your name")
    p.add_argument("--shout", action="store_true", help="Uppercase greeting")
    args = p.parse_args()

    msg = greet(args.name)
    if args.shout:
        msg = msg.upper()
    print(f"{msg} (v{__version__})")

`README.md`

Explain in 4–6 lines what the tool does and show one example command.

📖 `pyproject.toml` with setuptools

This file tells build tools how to package your project.

[build-system]
requires = ["setuptools>=68", "wheel"]
build-backend = "setuptools.build_meta"

[project]
name = "dmagogreet"
version = "0.1.0"
description = "A tiny Digital Mago greeting CLI"
readme = "README.md"
requires-python = ">=3.8"
authors = [{ name = "Your Name", email = "you@example.com" }]
license = { text = "MIT" }
classifiers = [
  "Programming Language :: Python :: 3",
  "License :: OSI Approved :: MIT License",
  "Operating System :: OS Independent",
]

# No runtime dependencies for this tiny tool
dependencies = []

[project.scripts]
# Creates a console command named `dmagogreet`
dmagogreet = "dmagogreet.cli:main"

[tool.setuptools.packages.find]
include = ["dmagogreet*"]

Why this matters: project.scripts wires your main() to a real terminal command, so you can type dmagogreet anywhere after install.

📖 Build Your Package

Do these in your virtual environment from Day 16.

Install build tools:

pip install build twine

Build:

python -m build

This creates a dist/ folder with:

dmagogreet-0.1.0.tar.gz (sdist)
dmagogreet-0.1.0-py3-none-any.whl (wheel)

Try a Local Install

pip install dist/dmagogreet-0.1.0-py3-none-any.whl

Run your CLI:

dmagogreet YourName

Expected output:

Hello from Digital Mago, YourName! (v0.1.0)

Try the shout option:

dmagogreet YourName --shout

Expected output:

HELLO FROM DIGITAL MAGO, YOURNAME! (V0.1.0)

Uninstall during testing:

pip uninstall dmagogreet -y

📖 (Optional) Publish to TestPyPI

Create an account/token on the TestPyPI index.
Upload your files:

twine upload --repository testpypi dist/*

Test install from there (keeping the main PyPI for dependency fallback):

python -m pip install --index-url https://test.pypi.org/simple/ \
  --extra-index-url https://pypi.org/simple dmagogreet==0.1.0

Ready for the real thing later? Replace testpypi with the default repository:

twine upload dist/*

📖 Versioning & Metadata Tips

Use Semantic Versioning: MAJOR.MINOR.PATCH (e.g., 0.1.1 for small fixes).
Update both __version__ and project.version together.
Keep a friendly CHANGELOG.md.
Write a clear README with a quick start.
Include a LICENSE file (MIT is beginner‑friendly).

🧰 Troubleshooting

Command not found after install
Close and reopen your terminal, or ensure your virtual environment is active. On Windows, the script lives in env\Scripts; on macOS/Linux in env/bin.
Build fails
Check that pyproject.toml is valid TOML (matching quotes/brackets) and your package folder name matches include.
Upload denied
Make sure the version number is new (PyPI/TestPyPI doesn’t allow replacing the same version).

🧙‍♂️ Take the Wand and Try Yourself

Goal: Ship a tiny package with a CLI and install it locally.

Create the project layout shown above.
Fill in __init__.py, cli.py, pyproject.toml, and README.md.
Build with python -m build.
Install the wheel and run dmagogreet with and without --shout.
Bump the version to 0.1.1, rebuild, reinstall, and confirm the new version prints in the CLI output.
(Optional) Upload to TestPyPI and test remote installation.

Expected terminal output (abridged):

$ python -m build
... Successfully built dmagogreet-0.1.0 ...
$ pip install dist/dmagogreet-0.1.0-py3-none-any.whl
Successfully installed dmagogreet-0.1.0
$ dmagogreet YourName
Hello from Digital Mago, YourName! (v0.1.0)
$ dmagogreet YourName --shout
HELLO FROM DIGITAL MAGO, YOURNAME! (V0.1.0)

Up next: Day 26: Introduction to Frameworks — a tour of popular web and data frameworks and when to use each.

Day 25 of 30: 📦 Packaging & Distribution

Subscribe to keep reading

Keep Reading

Digital Mago