See Download and Install for the installation instructions. Since NiPy is provided within stock distribution (main component of Debian, and universe of Ubuntu), to install all necessary requirements it is enough to:
sudo apt-get build-dep python-nipy
Note
Above invocation assumes that you have references to Source repository listed with deb-src prefixes in your apt .list files.
Otherwise, you can revert to manual installation with:
sudo apt-get build-essential
sudo apt-get install python-dev
sudo apt-get install python-numpy python-numpy-dev python-scipy
sudo apt-get install liblapack-dev
sudo apt-get install python-sympy
Some functionality in NiPy requires additional modules:
sudo apt-get install ipython
sudo apt-get install python-matplotlib
sudo apt-get install mayavi2
For getting the code via version control:
sudo apt-get install git-core
Then follow the instructions at Submitting a patch.
And for easier control of multiple Python modules installations (e.g. different versions of IPython):
sudo apt-get install virtualenvwrapper