DIGITS depends on several python packages from PyPI.
The recommended installation method is to use a virtual environment. This separates your python packages for DIGITS from any other packages you have installed on your system.
% pip install virtualenv
Change into the directory for your DIGITS installation and create the virtual environment there (or wherever else you like):
% cd $DIGITS_HOME
% virtualenv venv
% source venv/bin/activate
Now your path has been updated to use python and pip from your virtual environment:
$ which python
/home/username/digits/venv/bin/python
$ which pip
/home/username/digits/venv/bin/pip