The main purpose of this package is to provide more complex arithmetic operations on dates/times. Heavy use is made of the relativedelta type from Labix's dateutil library. Much of this package is just a light wrapper on top of this with some added features such as range generation and business day calculation.
You should install dateutils with pip:
pip install dateutils
Otherwise, you'll have to download the package and run:
python setup.py install
If you install it this way then you will also have to install all necessary dependencies manually.