jjjermiah / learn-pixi

Learning Pixi

Proposal Design

• environment set mechanism
• clear, conflict free management of dependencies tailored to specific environments while also maintaining the integrity of fixed lockfiles

There are multiple scenarios where multiple environments are useful.

• Testing of multiple package versions, e.g. py39 and py310 or polars 0.12 and 0.13.
• Smaller single tool environments, e.g. lint or docs.
• Large developer environments, that combine all the smaller environments, e.g. dev.
• Strict supersets of environments, e.g. prod and test-prod where test-prod is a strict superset of prod.
• Multiple machines from one project, e.g. a cuda environment and a cpu environment.

Features and Environments

dependencies: The conda package dependencies pypi-dependencies: The pypi package dependencies system-requirements: The system requirements of the environment activation: The activation information for the environment platforms: The platforms the environment can be run on. channels: The channels used to create the environment. Adding the priority field to the channels to allow concatenation of channels instead of overwriting. target: All the above features but also separated by targets. tasks: Feature specific tasks, tasks in one environment are selected as default tasks for the environment.

[dependencies] # short for [feature.default.dependencies]
python = "*"
numpy = "==2.3"

[pypi-dependencies] # short for [feature.default.pypi-dependencies]
pandas = "*"

[system-requirements] # short for [feature.default.system-requirements]
libc = "2.33"

[activation] # short for [feature.default.activation]
scripts = ["activate.sh"]

[feature.py39.dependencies]
python = "~=3.9.0"
[feature.py310.dependencies]
python = "~=3.10.0"
[feature.test.dependencies]
pytest = "*"

Define tasks as defaults of an environment

[feature.test.tasks]
test = "pytest"

[environments]
test = ["test"]
# `pixi run test` == `pixi run --environment test test`

Testing a production envirronment with additional dependencies

[environments]
# Creating a `prod` environment which is the minimal set of dependencies used for production.
prod = {features = ["py39"], solve-group = "prod"}
# Creating a `test_prod` environment which is the `prod` environment plus the `test` feature.
test_prod = {features = ["py39", "test"], solve-group = "prod"}
# Using the `solve-group` to solve the `prod` and `test_prod` environments together
# Which makes sure the tested environment has the same version of the dependencies as the production environment.

User Interface Environment Activation

Users can manually activate the desired environment via command line or configuration

• guarantees a conflict-free environment by allowing only one feature set to be active at a time
• for the user, the cli would look like this:

default

pixi run python
# Runs python in the 'default' environment

specific environment

pixi run -e test pytest
pixi run --environment test pytest
# Runs pytest in the 'test' environment

activating a shell in an environment

pixi shell -e cuda
pixi shell --environment cuda

running any command in an environment

pixi run -e env python
pixi run --environment env python

7 reasons to switch from conda to pixi

link

First of all its Faster - Pixi is 10x faster than conda

• integrated with pypi more deeply, which allows for faster dependency resolution

Painlessly switch from conda to pixi

• A single command pixi init --import ./myenv.yml should bring all dependencies from an existing conda environment.yml file to a newly created pixi.toml.

Reason 1: Work Faster

Reason 2: Better Integration with PyPi

• deeper resolution using Rust's uv resolver
• pypi packages are also locked alongside conda

Reason 3: No more miniconda base environment

pixi is a statically linked binary, which means it doesn't need a base environment to run.

• optimized for speed and compatability
• no messy base environment or miniconda/miniforge shell script installation

# Linux & macOS
curl -fsSL https://pixi.sh/install.sh | bash
# Windows
iwr -useb https://pixi.sh/install.ps1 | iex

Reason 4: Install your favorite tools globally

conda-forge tools such as git, bat, rg, bash can be installed globally with pixi

each globally installed tool lives in its own isolated environment

pixi global install git bash ripgrep bat

Reason 5: Sidestep activation

no "conda activate" or "conda deactivate" needed

• project should define all configurations in a pixi.toml file and run pixi shell or pixi run

Reason 6: Use tasks to easily collaborate

unique to Pixi are tasks which are simple entry points to a project such as start build lint Instead of writing Makefiles or bash scripts with complicated installation instructions you can make everything work cross-platform with pixi tasks

Reason 7: Native lockfiles

Pixi natively creates and uses lockfiles with lots of inspiration from conda-lock, poetry, cargo, and other modern package managers.