EXOZIPPy

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This will eventually be a python successor to EXOFASTv2, but it is not officially released yet. Many features are missing, not tested, or not functional. If you'd like to help with development, please contact me at jason.eastman@cfa.harvard.edu

Installing

EXOZIPPy is on PyPI. Only pre-releases exist so far, so --pre is required -- without it pip reports that no matching version exists:

pip install --pre exozippy

All dependencies resolve from PyPI, so no compiler is required to install on the supported platforms below (a compiler and the Python headers are still needed at runtime -- see "Runtime requirements" under Supported platforms). A nightly CI job installs exactly this way, with no lock file, to check that a fresh install keeps working as upstream packages move.

For development

Use Poetry, which installs the pinned poetry.lock and so reproduces a known good dependency set:

conda create -n exozippy python=3.12
conda activate exozippy
git clone https://github.com/jdeast/EXOZIPPy.git
cd EXOZIPPy
poetry install --extras gui
poetry run pre-commit install

--extras gui is worth taking even if you never open the GUI (and you probably should not -- see "The GUI is experimental" below): ruamel-yaml lives in that extra, and without it roughly 30 tests fail at import.

See CONTRIBUTING.md for the workflow (master is protected; changes go through a pull request with a passing test suite).

Supported platforms

Every push and pull request runs the full test suite on:

OS	Python
Linux (ubuntu-latest)	3.12, 3.13, 3.14
macOS (arm64)	3.12

Intel Macs: supported, with two gaps and an extra install step

macOS x86_64 works, on Python 3.12 or 3.13, and a separate CI job (macos-15-intel, nightly and on every pull request) keeps it that way. Two features are unavailable there, and the install needs one extra command before poetry install. Both gaps trace to a single upstream fact -- jaxlib's last macOS x86_64 wheel is 0.4.38 and jaxlib ships no sdist, so no newer jax can be installed on that hardware at all:

• the gp: key (Gaussian-process noise) is unavailable, because celerite2's PyMC backend imports jax at module scope;
• the numpyro and blackjax samplers are unavailable. Use nuts, ptde (the default) or nutpie, none of which touch jax.

Everything else -- RV, transit, SED, astrometry, microlensing -- works normally. The runbook, the reasoning, and the upstream fixes that will remove the extra step are in MACOS_INTEL_INSTALL.md. Apple Silicon Macs need none of this; check with uname -m.

Windows: supported through WSL2

Windows is supported, via WSL2 (Windows Subsystem for Linux) -- not natively. That is not a hedge: inside WSL2 you are running a real Linux kernel with a genuine Ubuntu userspace, so it is the Linux platform in the table above, fork-based samplers and all. A full development setup there passes 1272 of 1272 tests. The step-by-step runbook, verified end to end on a real machine (Windows 11 -> Ubuntu 26.04 -> Python 3.14 -> Poetry), is WINDOWS_INSTALL.md.

Minimum Windows version

WSL2 requires build 19041 or newer (Windows 10 version 2004, the May 2020 Update) or any Windows 11. Check with winver, or from PowerShell:

[System.Environment]::OSVersion.Version

Note: Microsoft numbers Windows 10 releases YYMM, so "version 2004" means April 2020, not the year 2004. Build numbers are less ambiguous and are what this document uses.

Builds 18362 and 18363 (versions 1903 and 1909) can also run WSL2 on x64 if fully patched, but wsl --install does not exist there and the manual setup is not covered here.

Below that there is no way to run EXOZIPPy on Windows: native Windows cannot run the samplers (below), and WSL1 is a syscall translation layer rather than a Linux kernel. Windows 7, 8, 8.1 and early Windows 10 are therefore unsupported, as is any Windows 10 after its October 2025 end of support. On hardware that cannot take a current Windows, install Linux directly -- it is the platform EXOZIPPy is developed and tested on, and it will outperform a VM on old machines.

Why not natively? Two independent reasons:

1. The PTDE sampler cannot work. It builds worker pools with multiprocessing's fork start method so children inherit the compiled PyTensor logp function without pickling it -- cloudpickle cannot serialize one. Windows has no fork, only spawn.
2. The suite never finished. It took over 90 minutes against ~16 on Linux and never completed a CI run, so the job was removed rather than left producing no signal. Three real Windows bugs were found and fixed along the way (an unsatisfiable mkl pin, a POSIX-only SIGALRM in the symbolic solver, and a cross-process stop signal), so basic use may well work -- but nothing verifies it.

Native Windows would additionally need a GCC-style C++ compiler for PyTensor's runtime compilation (MSVC will not do), which we have never tested. See notes/todo.txt if you want to pick native Windows up -- patches welcome.

Quickstart

Open an administrator PowerShell (Start menu, type "powershell", then "Run as administrator") and run:

wsl --install

Reboot -- the optional components only activate then, and without it wsl --status claims virtualization is disabled even when it is not. Open the Ubuntu app once to create a Unix user, then inside Ubuntu:

sudo apt update
sudo apt install -y g++ python3-dev python3-venv
python3 -m venv ~/exozippy-env
source ~/exozippy-env/bin/activate
pip install --pre exozippy

Note python3, not python: see the PATH note below. python3-venv is not optional -- without it python3 -m venv fails on ensurepip.

What WSL2 costs you

One thing genuinely bites, and it is a resource default rather than a missing feature:

• Memory. WSL2 takes 50% of host RAM by default. On a 16 GB laptop that is ~7.6 GB, while pyproject.toml asks for -n 6 test workers that each peak at 1-2 GB compiling PyTensor graphs. Measured on that machine, available memory bottomed out at 41 MB: workers were killed ([gwN] node down), xdist died in its own scheduler, and one run hung for hours. Fix it with a .wslconfig (see the runbook) or run -n 2 as CI does.

Smaller, setup-time only:

• Windows PATH is appended to the Linux one, so bare python/pip/npm resolve to Windows executables -- which is how poetry install can install nothing and still exit 0.
• There is no full systemd session, so apt prints harmless Failed to connect to system scope bus warnings.
• Keep the repo on the Linux filesystem, not /mnt/c, where I/O is far slower.

Not limitations: fork works (so PTDE and its tests run), PyTensor compiles C at runtime, and the whole suite passes. GPU/CUDA for the JAX samplers is untested.

The end-user path above (pip install --pre exozippy inside WSL) is enough to run fits. For a development checkout -- git clone plus Poetry plus the test suite -- follow WINDOWS_INSTALL.md, which covers the traps above in order.

Intel macOS is untested here and needs a C++ compiler: exoplanet-core publishes wheels for CPython 3.12-3.14 on Linux (glibc 2.28+), Apple Silicon macOS and Windows, but not Intel macOS, so it builds from source there.

Runtime requirements

PyTensor compiles C code at runtime, so running a fit needs a C++ compiler and the Python development headers -- even though pip install itself succeeds without them. Missing headers show up as a CompileError ending in fatal error: Python.h: No such file or directory the first time a model is built. This is common on RHEL-family systems, where the headers ship in a separate package from Python itself. To install both:

# RHEL / Rocky / Alma / CentOS / Fedora (match the -devel version to your Python)
sudo dnf install gcc-c++ python3.12-devel

# Debian / Ubuntu
sudo apt install g++ python3.12-dev

macOS's Xcode Command Line Tools (xcode-select --install) and any conda Python (e.g. the Miniforge setup above) already include the headers. So if you lack root on a Linux box, building your environment from a conda Python instead of the system one sidesteps the problem entirely (conda can also supply the compiler itself if the box has none):

conda create -n exozippy python=3.12
conda activate exozippy
pip install --pre exozippy       # or the Poetry development setup above

If the toolchain is broken anyway (no g++, or g++ without Python.h), exozippy detects it at startup, prints a warning naming the fix, and falls back automatically to PyTensor's much slower pure-Python mode -- usable as a smoke test, not for a real fit. (Setting PYTENSOR_FLAGS="cxx=" by hand is not enough: models with more than ~31 likelihood terms then die on numpy's 32-operand ufunc limit; the automatic fallback also installs the graph rewrite that works around it.)

Running a fit

cd examples/ob140939
exozippy ob140939.yaml

The GUI is experimental

There is an optional browser GUI (installed by the gui extra), started with:

exozippy-gui

Treat it as experimental on every platform, including Linux and macOS. It is still buggy and has never been verified driving a real fit end to end, so it is not part of what "supported" means above -- unlike the CLI, nothing in CI exercises it beyond unit tests of its own modules. Use it to look around; do not rely on it for science.

Note this is a statement about the GUI everywhere, not a WSL caveat.