/usr/lib/python2.7/dist-packages/zope.principalregistry-3.7.1.egg-info/namespace_packages.txt is in python-zope.principalregistry 3.7.1-0ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/zope.principalregistry-3.7.1.egg-info/../../../../share/pyshared/zope.principalregistry-3.7.1.egg-info/namespace_packages.txt