Nox is a command-line tool that automates development tasks like testing and linting across multiple Python environments. It utilizes a standard Python file (`noxfile.py`) for configuration, creating isolated virtual environments for each defined session. This approach provides programmatic control and reproducibility, installing specified dependencies and running commands within each isolated environment. As of version 2026.2.9, Nox is actively maintained with a regular release cadence, often following a calendar versioning scheme.
pip install noxVerified import paths — ran on the pinned version, not inferred.
Create a `noxfile.py` in your project root to define test, lint, and format sessions. Nox will automatically create isolated virtual environments for each session, install dependencies, and execute commands. Run `nox` to execute all defined sessions, or `nox -s <session_name>` to run a specific one.
Update `pip install` commands to `pip install nox`, rename `nox.py` to `noxfile.py`, and rewrite session configurations to use imperative `session.install()` and `session.run()` calls. Ensure Python 3.5+ is used for Nox itself.
Install `nox` using `pip install nox` (preferably `pipx install nox`) outside of any project-specific virtual environment. Do not add `nox` to your project's `requirements.txt` or `pyproject.toml` dependencies.
Always include `session.install('your-dependency')` at the beginning of your Nox session functions for all required packages. Do not rely on packages being available from your global environment or other sessions.If encountering issues with `uv` environments not clearing as expected, ensure your `noxfile.py` or `nox` configuration that uses `uv` backend accounts for this change. Nox 2026.2.9 was released to support this `uv` change internally.
Ensure 'nox' is installed in an environment accessible from your system's PATH, or invoke it using `python -m nox`. If using a virtual environment, activate it before running `nox`.
Install the required Python interpreter (e.g., using pyenv, conda, or system package manager) and ensure it's accessible in your system's PATH, or configure nox to download interpreters using `--download-python`.
First, verify that `noxfile.py` exists at the expected path. If it does, meticulously debug `noxfile.py` for syntax errors, incorrect imports, or any `FileNotFoundError`s or other exceptions within its logic that prevent it from being loaded.
Ensure all necessary tools and packages are explicitly installed within the Nox session using `session.install()`. For system-wide tools, confirm they are correctly installed and available in the system's PATH.
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