Install and data

Install the package, then download the datasets you need once.

pip install cosmonuts            # or: uv add cosmonuts
cosmonuts --version

Extras

The core install runs the bundled W0WaCDM theory with BAO and supernova likelihoods. Everything else is an optional extra, imported only when you use it:

Extra	Adds	Needed for
classe	class-e emulators	ClassETheory, binned \(P(k)\), CMB spectra
eft4py	eft4py	EFT4PyTheory, DESIDR1ShapeFit
desi	h5py	DESI data files
clipy	clipy-like	Planck 2018 .clik likelihoods
candl	candl-like	ACT and SPT likelihoods
mpi	mpi4py	parallel="mpi"
gpu	jax[cuda13]	NVIDIA GPUs (Linux)

pip install 'cosmonuts[classe,clipy]'

Theory backends stay optional

class-e and eft4py are never required. Their modules are imported lazily, so a missing backend only fails when you ask for it, with a message naming the extra.

Data

cosmonuts install downloads the data of the bundled likelihoods:

cosmonuts install desi_dr2_bao des_dovekie desi_dr1
cosmonuts install pantheon_plus union3 union3.1
cosmonuts install --all --path ~/cosmo_data
cosmonuts install --help          # lists each dataset and whether it is installed

The packages path is, in order, --path, the COSMONUTS_PACKAGES_PATH environment variable, then the platform's user data directory. From Python: install, is_installed and packages_path. A likelihood whose data are missing raises DataNotFoundError.

Likelihoods

Dataset (cosmonuts install)	Likelihood classes
desi_dr2_bao	DESIDR2BAO
desi_dr1	DESIDR1BAO, DESIDR1ShapeFit
des_dovekie	DESDovekie
pantheon_plus	PantheonPlus, PantheonPlusSH0ES
union3, union3.1	Union3, Union31
planck_2018_clik	PlanckLowlTT, PlanckLowlEE, PlanckPlikLiteTTTEEE (extra clipy)
none	PlanckPR4EarlyLCDM: three numbers shipped with the package
user data	ClipyLikelihood (any .clik file), CandlLikelihood (extra candl)

cosmonuts info likelihoods prints the same list from your installation.