Enhancement: python.uv_venv_auto should take into account UV_PROJECT_ENVIRONMENT

[rsyring]

uv's default is to use .venv for a project's virtualenv. However, a different path can be provided by using UV_PROJECT_ENVIRONMENT.

Currently, mise doesn't check for an alternate location.

This is probably obvious, but the variable being used should come from the result of mise's environment variable processing pipeline.

My current workaround is to set:

[env]
_.python.venv.path = '{{ env.UV_PROJECT_ENVIRONMENT }}'
_.python.venv.create = true

But it would be cleaner if I could just:

[settings]
python.uv_venv_auto = true

and trust that whatever uv is doing, mise will play along.

FWIW, my higher-level goal is to support some of our users wanting to use .venv and some users wanting to put those files in a temporary/cache location. So, our actual project files look like:

[env]
VENV_IDENT = 'foo-app'

_.python.venv.path = '{{ env.VIRTUALENV_DIR }}'
_.python.venv.create = true

And then ~/mise.toml has:

[env]
VIRTUALENV_DIR = '.venv'

or:

[env]
VIRTUALENV_DIR = { value='{% if env.VENV_IDENT %}~/.cache/venvs/{{ env.VENV_IDENT }}{% endif %}', tools = true }
UV_PROJECT_ENVIRONMENT = { value='{% if env.VIRTUALENV_DIR %}{{ env.VIRTUALENV_DIR }}{% endif %}', tools = true }

[rsyring]

@jdx with uv integration enhancements a stated goal for 2025, might this warrant an issue?

The workaround is ok, but it would be nice to be able to set python.uv_venv_auto at the user level and remove all venv activation config from a project's mise.toml.

Thanks for considering.

[rsyring]

FWIW, here is how I'm currently handling this to get support for devs who do and don't want to use a local .venv:

# ~/.config/mise.toml

[env]
UV_PROJECT_ENVIRONMENT = { value='{% if env.PROJECT_SLUG %}/home/rsyring/.cache/uv-venvs/{{ env.PROJECT_SLUG }}{% endif %}', tools = true }

[settings]
python_venv_auto_create = true

And then in a project's mise.toml:

PROJECT_SLUG = '{{ config_root | basename | slugify }}'

_.python.venv.path = '{% if env.UV_PROJECT_ENVIRONMENT %}{{ env.UV_PROJECT_ENVIRONMENT }}{% else %}.venv{% endif %}'
_.python.venv.create = true

Would still be nice to see mise recognize UV_PROJECT_ENVIRONMENT and use it for the Python venv path.

The upstream solution would be for uv to support a centralized location for virtualenvs. That is being tracked at: astral-sh/uv#1495

[Marukome0743]

This is supported now following PR #11475.

With current mise, python.uv_venv_auto = true honors UV_PROJECT_ENVIRONMENT when selecting the project virtualenv path. The value can come from either the process environment or mise’s processed config environment, so a user-level configuration can provide the custom path without requiring each project to repeat the explicit _.python.venv.path directive.

For example:

[env]
UV_PROJECT_ENVIRONMENT = "/path/to/custom/venv"

[settings]
python.uv_venv_auto = true

Updating to a current mise release should allow the simpler configuration requested here.

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