Custom CLASS builds¶

Use any classy build (AxiCLASS, Hi-CLASS, CLASS-EFT, a modified fork) without touching the installed one.

Selecting the build¶

Precedence, highest first:

--classy PATH on class-e generate
the CLASS_E_CLASSY environment variable
theory.classy.path in the YAML
the classy installed in the environment

PATH can be a CLASS source tree, a site-packages or build/lib.* directory containing classy, or the compiled classy*.so itself.

theory:
  classy:
    path: /path/to/AxiCLASS

class-e generate configs/ede-axiclass.yaml --classy ~/github/AxiCLASS

The choice is propagated to the worker processes, so every chunk uses the same build.

Building CLASS with Python support¶

cd /path/to/CLASS
make clean && make
python setup.py build        # creates build/lib.<platform>-<python>/classy*.so

The build must match the Python version running class-e.

From Python¶

The class-e functions that run CLASS (get_observables, compute_cosmology, compute_dataset) use the selected build. Without an explicit choice, the first CLASS run uses CLASS_E_CLASSY if it is set, and the installed classy otherwise. To choose a build in code, or to honour a YAML's theory.classy.path, select it before the first run (a process holds one CLASS):

from class_e.core.boltzmann import classy_info, resolve_classy_path, select_classy
from class_e.utils.yml import load_yaml

# either the CLI's precedence (--classy, CLASS_E_CLASSY, theory.classy.path, installed) ...
select_classy(*resolve_classy_path(model_data=load_yaml("configs/ede-axiclass.yaml")))
# ... or a build by path:  select_classy("/path/to/AxiCLASS")
print(classy_info())                  # version, file and where the choice came from

For CLASS's own Class from a given build:

from class_e.utils import load_class_from_path

Class = load_class_from_path("/path/to/AxiCLASS")
cosmo = Class()

Troubleshooting¶

Message	Cause and fix
`No directories starting with 'lib' were found`	CLASS was not built. Run `python setup.py build` inside the CLASS directory.
`Could not import classy module`	The build targets another Python version. Rebuild with the interpreter you run `class-e` with.
`No suitable compiled import path found`	`build/lib.*` exists but contains no `.so`, `.pyd` or `.dylib`. Rebuild and check the compiler output.