Using `uv` and `just` to manage Python virtual environments • Duckling Gazette

Over time, I tried lots of tools to manage my Python virtual environments, but I didn’t end up liking any of them:

python -m venv is too “manual” for me, and I usually want my virtual environments all in one place;
virtualenvwrapper is a 1.4k-lines Bash script - I want something simple and solid;
pew worked for me, but it’s a lot more complex than what I need.

I decided to write my own, and started to brainstorming what I wanted from my “venv manager”.

Designing the perfect venv manager 📐

I came up with a few requirements:

it should be very simple and self-contained;
it should allow me to easily create, activate, list, and delete virtual environments;
it should be fast;

Luckily, there are two tools for the job: uv and just.

uv is “an extremely fast Python package and project manager, written in Rust” (from their GitHub description). It’s so fast that in lots of cases it removes the need for virtual environments entirely - you can just create an ephemeral one and istall the dependencies almost instantly. With uv venv you can create virtual environments very easily, and after activating you can uv pip install (or just pip install) everything you need.
While uv addresses a part of my requirements (venv creation, speed), it doesn’t cover all on its own.

just is a command runner inspired by make: this makes its syntax extremely familiar, and it brings a lot of quality-of-life improvements to the table. Among other things, just allows you to define recipes that accept arguments, and to effectively show and document the available commands with just --list.

Both of them are in Snapcraft, so you can easily install them with:

snap install astral-uv
snap install just

Putting the pieces together 🧩

This is the uv-venv script that lives somewhere in my PATH:

#!/usr/bin/env -S just --justfile
set quiet

uv := `which uv` # require `uv`
venv_home := env('WORKON_HOME') # require env variable

[private]
default:
  echo "Virtual Environment manager - in Just!\n"
  just --justfile={{justfile()}} --list

# Create a new virtual environment under {{venv_home}}
new name:
  uv venv --allow-existing --relocatable --no-config --directory="{{venv_home}}" "{{name}}"

alias rm := remove
# Remove a virtual environment from {{venv_home}}
remove name:
  echo "Removing {{venv_home}}/{{name}}"
  rm -rI "{{venv_home}}/{{name}}"

alias ls := list
# List all the virtual environments in {{venv_home}}
list:
  ls "{{venv_home}}"

# Activate a virtual environment
activate name:
  #!/usr/bin/env bash
  source "{{venv_home}}/{{name}}/bin/activate"
  exec $SHELL -i

Let’s go over the different sections of the script.

set quiet makes recipes silent by default, so they are not printed before being executed;
uv and venv_home are Just variables; just will fail if which uv fails (effectively enforcing it as a requirement), or if WORKON_HOME is not an environment variable;
the default recipe is what’s executed when I run the script without any recipe: it will show all the available recipes next to their verbose explanation;
the other recipes are pretty self-explanatory;
alias allows to call a recipe via multiple names: uv-venv list and uv-venv ls will both run the list recipe.

If I run it, it displays the following (with colored output):

∮ uv-venv
Virtual Environment manager - in Just!

Available recipes:
    activate name # Activate a virtual environment
    list          # List all the virtual environments in {{venv_home}}
    ls            # alias for `list`
    new name      # Create a new virtual environment under {{venv_home}}
    remove name   # Remove a virtual environment from {{venv_home}}
    rm name       # alias for `remove`

Conclusions 🌷

This little script made my workflows a lot faster, it’s tiny (30 lines of code!), and it does exactly what I wanted.

Hope it’s useful for you too!