The simplest way to install Cosmic Ray is with
pip install cosmic_ray
This will install the most recent uploaded version in PyPI.
If you want to install Cosmic Ray from source you need to use
python setup.py install
You’ll often want to install Cosmic Ray into its own virtual environment. In earlier versions we suggested installing Cosmic Ray into the same environment as the project being tested, but that’s no longer the case. In recent versions, Cosmic Ray will create temporary virtual environments for the code under test, so the environments for Cosmic Ray and the code under test are safely separated.