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Module 11 / Project 01 — Package Structure

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Focus

  • The src layout for Python packages
  • pyproject.toml configuration
  • __init__.py and what it does
  • Entry points (console scripts)

Why this project exists

Before you can share your code as a pip-installable package, you need to structure it correctly. This project builds a real package from scratch and explains every file.

Run

cd projects/modules/11-package-publishing/01-package-structure
python -m mymath.calculator

Expected output

mymath calculator v0.1.0
add(2, 3) = 5
subtract(10, 4) = 6
multiply(3, 7) = 21
divide(15, 4) = 3.75

Project structure

01-package-structure/
├── pyproject.toml         # Package metadata and build config
├── README.md              # This file (also rendered on PyPI)
├── LICENSE                # MIT license
├── src/
│   └── mymath/
│       ├── __init__.py    # Makes mymath a package, exports version
│       ├── calculator.py  # Core math functions
│       └── statistics.py  # Mean, median, mode functions
└── tests/
    ├── test_calculator.py
    └── test_statistics.py

Alter it

  1. Add a new module src/mymath/geometry.py with area_circle() and area_rectangle(). Update __init__.py to export it.
  2. Add a console script entry point in pyproject.toml so you can run mymath-calc from the command line.
  3. Change the version to 0.2.0 and add a __version__ attribute.

Break it

  1. Remove __init__.py. Can you still import mymath?
  2. Put files directly in mymath/ instead of src/mymath/. What changes?
  3. Delete pyproject.toml. Can you still run the code? Can you build a package?

Fix it

  1. Restore __init__.py and verify imports work again.
  2. If using flat layout, update pyproject.toml to find packages correctly.
  3. Recreate pyproject.toml with the minimum required fields.

Explain it

  1. Why does the src layout exist? What problem does it solve?
  2. What is the difference between a module and a package?
  3. What does __init__.py do when you import mymath?
  4. What is an entry point and why would you use one?

Mastery check

You can move on when you can: - create a package with the src layout from memory, - explain what pyproject.toml fields are required, - add a new module and export it from init.py, - write tests for your package.

Next

Project 02 — Build and Test