PhysicalQuantities is a python module that allows calculations to be aware of physical units. Built-in unit conversion ensures that calculations will result in the correct aggregate unit.
The module also contains an extension for IPython. This allows greatly simplified use by typing in physical quantities directly as number and unit.
The documentation is contained in IPython notebooks: http://nbviewer.ipython.org/github/juhasch/PhysicalQuantities/blob/master/doc/Index.ipynb
This module is based on the IPython extension by Georg Brandl: https://bitbucket.org/birkenfeld/ipython-physics. It was converted into a standalone Python module and extended heavily.