Errata

In Chapter 8 of my book, the shapefile doesn't have a .prj file which isn't a big deal for the example

but can be annoying if you try to open it in QGIS or ArcGIS.  There was also an unused numpy array in the example so I updated the whole package.  You can download the updated script and data here:
https://geospatialpython.googlecode.com/svn/NDVI-update.zip

This example is the very first example in the chapter.  The second example shows you how to classify the output data to create the image shown here.