Developer Installation

To develop new code for CCL, you need to install it using pip’s development install. This installation method creates a symbolic link between your Python site-packages directory and the copy of CCL you are working on locally. Thus when you change CCL Python code, you do not need to reinstall CCL in order for the changes to be visible system-wide. Note, if you change the CCL C code, you will need to force CCL to recompile the code (and copy the resulting .so into the Python package) by rerunning the command below.

To install CCL using a pip developer installation, you can execute

$ pip install --no-deps -e .

from the top-level directory in the repository. You will need CMake in order to install CCL in this way. See Getting CMake for help installing CMake if you do not already have it. In order to run the tests, you will need CAMB, CLASS, and FAST-PT installed. See the instructions for Getting a Boltzmann Code and Getting FAST-PT for details.

C-layer Dependencies and Requirements

CCL has several C dependencies. The CMake build will download and compile these automatically if they are not present on your system. However, if you do have them installed locally in a spot accessible to CMake, the local versions will be used.

These dependencies are

  • GNU Scientific Library GSL, version 2.1 or above
  • FFTW3 version 3.1 or above
  • CLASS version 2.6.3 or above
  • SWIG

Uninstalling CCL in Developer Mode

To uninstall CCL in developer mode, simply type

$ pip uninstall pyccl

Boostrapping a CCL Development Environment with conda

One of the easier ways to get started with CCL development is to use conda-forge to provide the third-party requirements above and the necessary compilers. The following commands will get you started with a conda-forge-based development environment. Note that before you start, make sure to follow the conda-forge instructions for use and that your PYTHONPATH variable is not set.

Then do the following

$ conda create -n ccl-dev compilers cmake swig pyccl pytest flake8
$ conda activate ccl-dev
$ conda uninstall pyccl --force
$ git clone
$ cd CCL
$ pip install --no-deps -e .

This set of commands leaves a copy of the compiled C extension in the checked out copy of the code, e.g.,

$ ls pyccl/*.so

If you make changes to the C library or checkout a new branch, simply rerun pip install --no-deps -e . to rebuild the library.