Configure the Project to be Buildable

[ghickman]

This sets up the requisite config to make v2 pip installable. There are a couple of commits to change how the CLI and an import work to make that happen.

I've opted to use modern build tooling because we're not tied to older python versions or environments (yet). The metadata was generated by flit locally, but we don't need it installed to build artefacts, build can handle that, and pip install works without either. All build metadata is contained in pyproject.toml, and documented by flit here. Production requirements have been moved to pyproject.toml, and the Justfile updated to use pyproject.toml as the spec file for pip-compiling prod requirements.

[benbc]

@ghickman I don't have time to review this now, but we should check that IDEs understand how to install dependencies from pyproject.toml. I can check PyCharm on Monday.

[ghickman]

I've been testing this locally with a clean virtualenv and installing from the tarball of this branch:

rm -rf venv
python -m venv venv
venv/bin/python -m pip install https://github.com/opensafely-core/cohort-extractor-v2/archive/refs/heads/make-buildable.tar.gz#egg=cohortextractor
venv/bin/cohortextractor -h

[ghickman]

Discussion with @bloodearnest led to:

• discovering pip-compile --output-file=requirements.prod.txt pyproject.toml is a thing we can do
• reworking the PR to use that, which reverts all the Dockerfile and nearly all Justfile changes

[ghickman]

we should check that IDEs understand how to install dependencies from pyproject.toml.

@benbc – I didn't think too much about this last week, but is that a common flow? I've not come across it in Python land! I would expect it to work because the IDE must still be using a local venv/pip to install things? (surely 😰) We should still check of course 🙂

[benbc]

@ghickman Having looked at this a bit more, I think PyCharm is just integrating with the venv. I think it can do some pip-compile stuff too, but that's much less important. Nothing for you to worry about here.