/usr/lib/python2.7/dist-packages/mx/NewBuiltins.py is in python-egenix-mxtools 3.2.1-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/mx/../../../../share/pyshared/mx/NewBuiltins.py