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Module 11 / Project 02 — Build and Test

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— This project — — Flashcards — —

Focus

  • Building a wheel and sdist with python -m build
  • Installing your package locally with pip install -e .
  • Testing the installed package
  • Understanding dist/ contents

Why this project exists

Before publishing a package, you need to build it and verify it works when installed. This project walks through the build process and explains what the output files are.

Run

cd projects/modules/11-package-publishing/02-build-and-test

# Step 1: Build the package from project 01
cd ../01-package-structure
python -m build

# Step 2: Look at what was built
ls dist/

# Step 3: Install locally in editable mode
pip install -e .

# Step 4: Test the installed package
pytest tests/ -v

# Step 5: Use it from anywhere
python -c "from mymath import add; print(add(10, 20))"

Expected output

# After build:
dist/
  mymath_demo-0.1.0-py3-none-any.whl
  mymath_demo-0.1.0.tar.gz

# After pytest:
tests/test_calculator.py::test_add PASSED
tests/test_calculator.py::test_subtract PASSED
...
6 passed

# After import:
30

Project files

This project is a guide — the code lives in project 01. The script below automates the build-and-test workflow.

Alter it

  1. Modify a function in project 01, rebuild, and verify the change shows up when imported.
  2. Build without --wheel to get only an sdist. Compare the file sizes.
  3. Install the wheel directly with pip install dist/mymath_demo-0.1.0-py3-none-any.whl instead of editable mode.

Break it

  1. Delete pyproject.toml and try to build. What error do you get?
  2. Install in non-editable mode (pip install .) and then change a function. Does the change show up? Why not?
  3. Try to import mymath without installing it (from a different directory).

Fix it

  1. Restore pyproject.toml and rebuild.
  2. Reinstall with -e flag for editable mode, which picks up changes automatically.
  3. Add the src directory to PYTHONPATH as a temporary workaround.

Explain it

  1. What is the difference between a wheel (.whl) and an sdist (.tar.gz)?
  2. What does "editable mode" (pip install -e .) do differently from a normal install?
  3. Why does python -m build create both a wheel and an sdist?
  4. What is inside a wheel file? (Hint: it's a zip file — try renaming to .zip and opening it.)

Mastery check

You can move on when you can: - build a package from pyproject.toml, - install it locally in editable mode, - run tests against the installed package, - explain wheel vs sdist.

Next

Project 03 — Publish to PyPI