Normal procedure is to do "python setup.py build" as a
non-root user, doing only "python setup.py install" as
root.  If the non-root user has a restrictive umask
(i.e. 077), the built files will be mode 0600 (in
directories created 0700), etc, and "setup.py install"
will not make them world readable, so you end up with
things like doc files installed mode 0600 in a new
directory under /usr/share/doc/ that's mode 0700 and no
one but root can  read/use them.