nox-poetry

Use Poetry inside Nox sessions

This package provides a drop-in replacement for session.install in Nox sessions. It modifies its behavior in two ways:

• Packages are pinned to the versions specified in Poetry's lock file.
• The argument "." is replaced by a wheel built from the package.

Installation

Install nox-poetry from the Python Package Index:

$ pip install nox-poetry

Important: This package must be installed into the same environment that Nox is run from. If you installed Nox using pipx, use the following command to install this package into the same environment:

$ pipx inject nox nox-poetry

Usage

Invoke nox_poetry.patch() at the top of your noxfile.py, and you're good to go. nox-poetry intercepts calls to session.install and uses Poetry to export a constraints file and build the package behind the scenes.

If you prefer a less magical, more explicit approach, you can also invoke nox_poetry.install(session, ...) instead of session.install(...). Pass nox_poetry.WHEEL or nox_poetry.SDIST to build and install the local package using the specified distribution format.

Packages installed in this way must be managed as dependencies in Poetry.

For example, the following Nox session runs your test suite:

# noxfile.py
import nox
import nox_poetry

nox_poetry.patch()

@nox.session
def tests(session: Session) -> None:
    """Run the test suite."""
    session.install(".")
    session.install("pytest")
    session.run("pytest")

More precisely, the session builds a wheel from the local package, installs the wheel as well as the pytest package, and invokes pytest to run the test suite against the installation.

Why?

Consider what would happen in the above session with an unpatched session.install:

• Package dependencies would only be constrained by the wheel metadata, not by the lock file. In other words, their versions would not be pinned.
• The pytest dependency would not be constrained at all.
• Poetry would be installed as a build backend every time (although this could be avoided by passing the "--no-build-isolation" option).

Unpinned dependencies mean that your checks are not reproducible and deterministic, which can lead to surprises in Continuous Integration and when collaborating with others. You can solve these issues by declaring pytest as a development dependency, and installing your package and its dependencies using poetry install:

@nox.session
def tests(session: Session) -> None:
    """Run the test suite."""
    session.run("poetry", "install", external=True)
    session.run("pytest")

Unfortunately, this approach comes with its own set of problems:

• Checks run against an editable installation of your package, i.e. your local copy of the code, instead of the installed wheel your users see.
• The package is installed, as well as all of its core and development dependencies. This is wasteful when you only need to run black or flake8. It also goes against the idea of running checks in isolated environments.
• Poetry may decide to install packages into its own virtual environment instead of the one provided by Nox.

nox-poetry uses a third approach. Third-party packages are installed by exporting the lock file in requirements.txt format, and passing it as a constraints file to pip. When installing your own package, Poetry is used to build a wheel, which is then installed by pip.

In summary, this approach brings the following advantages:

• You can manage tools like pytest as development dependencies in Poetry.
• Dependencies are pinned by Poetry's lock file, making checks predictable and deterministic.
• You can run checks against an installed wheel, instead of your local copy of the code.
• Every tool can run in an isolated environment with minimal dependencies.
• No need to install your package with all its dependencies if all you need is some linter.

For more details, take a look at this article.

API

nox_poetry.patch(*, distribution_format=nox_poetry.WHEEL):

Monkey-patch nox.sessions.Session.install to use nox_poetry.install. The optional distribution_format parameter determines how to handle the special "." argument. By default, this is replaced by a wheel built from the package. Pass nox_poetry.SDIST to build an sdist archive instead.

nox_poetry.install(session, *args, **kwargs):

Install packages into a Nox session using Poetry.

The nox_poetry.install function installs dependencies into a Nox session, using the versions specified in Poetry's lock file. The function arguments are the same as those for nox.sessions.Session.install: The first argument is the Session object, and the remaining arguments are command-line arguments for pip install, typically just the package or packages to be installed. The constants WHEEL and SDIST are replaced by a distribution archive built for the local package. Keyword arguments are the same as those for nox.sessions.Session.run.

Contributing

Contributions are very welcome. To learn more, see the Contributor Guide.

License

nox-poetry is free and open source software, distributed under the terms of the MIT license.

Issues

If you encounter any problems, please file an issue along with a detailed description.

Credits

This project was generated from @cjolowicz's Hypermodern Python Cookiecutter template.