Using hatch to manage virtual environment without a build

[hallidave]

I have used hatch successfully in the past to build libraries, but I had the idea that maybe I could use it to purely manage my virtual environment for projects that don't need a build step (e.g. a Django project or just a one-off script).

I often just want to track a list of dependencies and/or target a Python version that is newer than the one offered by my Linux distribution.

So I tried this for my pyproject.toml file:

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[project]
name = "junk"
dependencies = [
  "numpy",
]

[tool.hatch.envs.default]
python = "3.12"

It almost works. If I run hatch env shell it installs the Python version I want and then errors out on the build step. If I run the command again, it syncs the dependencies and I have everything I need.

I tried adding skip-install = true to the default env config, but then the dependencies are never installed.

Does it make sense to support this use case? Maybe add an install-dependencies = true flag to go with the skip-install = true?

[ofek]

Hey there! For applications you would want to skip installation and also define dependencies for the environment itself rather than reusing that field meant for libraries/installable projects.

[hallidave]

Thanks for your reply.

Adding the dependencies to environment works, but I think it reduces the usefulness of the standard project file. For example, pip-tools uses the project dependencies to generate a requirements.txt. If the dependencies are moved to the environment, then tools dependent on the standard no longer work. It also removes the documentation advantage of separating development dependencies from project dependencies.

I found this example of someone using Hatch as a Django project tool: https://github.com/oliverandrich/django-hatch-startproject/blob/main/pyproject.toml. This is a more complex version of what I was trying to do. Hatch is great for documenting dependencies, matrix testing, and collecting development scripts together. It looks like this scenario used to work, but it no longer does.

If there was some config to say "I have no files to package" or "please install my project dependencies" that would be super useful.

[ofek]

The issue is that that standard is not meant for applications/environments, it's meant exclusively for packages that are used by others e.g. distributed on PyPI. This is a good writeup: https://snarky.ca/differentiating-between-writing-down-dependencies-to-use-packages-and-for-packages-themselves/

For compatibility you might be interested in this plugin instead https://github.com/repo-helper/hatch-requirements-txt

As far as that other project, you probably want the bypass-selection option as there was a change to make sure wheels couldn't be built empty (accidentally).

[hallidave]

Fair enough. Thanks for the additional context.

[hallidave]

Just wanted to add a quick follow up.

It turns out that the pyproject.toml I showed above works almost exactly how I want for simple, one-file scripts. The only change I needed to make was to give my script the same name as the project so that the default file selection of the wheel builder picks up my script. It is packaged and installed in my venv, which I don't strictly need, but it still does what I want in terms of managing the environment and documenting the python version and script dependencies. And it saves adding the extra config required to bypass selection or explicitly identify the file.

[ofek]

Have you tried this for one-off scripts? https://hatch.pypa.io/latest/how-to/run/python-scripts/

[hallidave]

What?! Can't believe I missed that. That's an excellent feature.