I assume in this answer that you want to use the client inside DSS (in a notebook or in a recipe). Remember that you should use the Python virtual environment of DSS (see How to install Python packages?).
git clone https://github.com/dataiku/dataiku-api-client-python cd dataiku-api-client-python python setup.py build cd /path/to/data_dir ./bin/pip install -e /path/to/dataiku-api-client-python
Note that on Mac OS X the data_dir is by default ~/Library/DataScienceStudio/dss_home/