Our manual links to the Python manual (or probably this is the Sphinx documentation). This is done with an intersphinx reference, part of which consists of fetching http://docs.python.org/objects.inv when one builds using "make" or "make [dir]html". This means that it is impossible to build Drizzle without network connection, (such as on an airplane, train) because failing to fetch that URL will make the build fail. (Warnings are errors.)
This changes the sphinx configuration file to use a local copy of the file instead, and adds the file to the repo. It is now possible to build Drizzle without network connection.
It will be necessary to update the local copy in docs/python-inv.txt from time to time.