# 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



## 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 https://github.com/LSSTDESC/CCL.git
$cd CCL$ 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
pyccl/_ccllib.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.