pixi and PyPilot

pixi is a package manager that installs from conda-forge and PyPI into a per-project environment, with a lock file. PyPilot supports pixi projects fully, and suggests pixi when a project hits a wall pip and uv cannot climb.

What ships when

Engine 1.2.0+ detects pixi projects and works through pixi (pixi install, pixi add --pypi, pixi add python=…, the .pixi/envs/default environment). The rest of this guide, marked 1.3 where it matters (the multi-environment and lock checks, the advisory, migrate-to-pixi, migrate-conda --to pixi, install-pixi, pixi_environment, package_manager = "pixi"), needs engine 1.3.0 or newer.

Why pixi helps

pip and uv install Python packages. They cannot install what a source build needs outside Python, and a dependency without a wheel for your platform is a source build.

Problem	With pip / uv	With pixi
Native libraries. GDAL, PROJ, HDF5, cairo, FFmpeg, eccodes…	The library must already be on the system, at the right version (gdal-config must match the bindings exactly)	conda-forge ships the library as a package next to the bindings
Compilers and Fortran. SciPy-stack packages without a wheel for your Python	A working C/C++/Fortran toolchain is needed	Prebuilt conda-forge binaries
The CUDA toolkit. Extensions with .cu sources need nvcc	Install the toolkit system-wide yourself	cuda-toolkit / cuda-nvcc from conda-forge, per project
More than Python. R, Rust, CMake/Meson C++ next to Python	Separate tools	One environment, one manifest
Reproducibility	uv has uv.lock; plain pip has none	pixi.lock for every platform listed in the manifest

pixi also installs Python itself, so the interpreter is part of the environment.

What PyPilot does in pixi projects

A folder is a pixi project when it has a pixi.toml, or a pyproject.toml with [tool.pixi.workspace]. PyPilot then works only through pixi, whatever package_manager says. Details in PyPilot in pixi projects.

• The environment is .pixi/envs/<name> (default unless pixi_environment says otherwise). Its Python, packages and GPU builds are read from there.
• Setup runs pixi install, installing a package runs pixi add --pypi, changing Python runs pixi add python=X.Y.
• No .venv is created, uv is not run, and pixi.lock is never written by PyPilot.
• doctor checks every environment, the lock, and every target platform.

~/src/px

$ pypilot doctor
PyPilot doctor: C:\src\px
  package manager : Auto

── Environment ──────────────────────────────────────────
  uv              : present (v0.13.5, on PATH)
  pixi env        : C:\src\px\.pixi\envs\default (Python 3.15)
  pixi project    : C:\src\px\pixi.toml
  interpreters    : 3.15 (python3), 3.14 (C:\Python314\python.exe)
  data tables     : refreshed 3 hours ago (next in 6 days); 1 of 5 bundled

── Project ──────────────────────────────────────────────
  files           : requirements.txt, pixi.toml
  pixi python     : python 3.15.*
  dependencies    : conda: requests, rich · pypi: httpx>=0.28.1,<0.29

── pixi ─────────────────────────────────────────────────
  platforms       : win-64
  pixi.lock       : up to date
  environments    :
    • default (selected)  Python 3.15  conda: requests, rich  pypi: httpx

── Compatibility ────────────────────────────────────────
  supported Python: 3.8–3.15
  recommended     : Python 3.15 (newest the dependencies support within pixi's `python 3.15.*`)
    • httpx                3.8–3.15

── Findings ─────────────────────────────────────────────
  ✓ Everything looks good.

When PyPilot suggests pixi 1.3

Outside pixi projects, PyPilot raises a "pixi can help here" finding when it sees a dependency with no installable wheel whose build needs native libraries that conda-forge provides, a failed build naming a missing header or library, CUDA sources without nvcc, or a repo that mixes Python with R, Rust or C++. See the advisory.

Moving a project to pixi 1.3

pypilot migrate-to-pixi (from pip/uv) and pypilot migrate-conda --to pixi (from environment.yml) preview a pixi.toml and write it only when asked. Your existing files are never edited or deleted. Step by step: Migrating to pixi.

No pixi installed?

PyPilot says so, changes nothing, and offers to install it: pypilot install-pixi, PyPilot: Install pixi in VS Code, or the Install pixi button in the notification. It runs pixi's official installer.