/usr/lib/python3/dist-packages/mpld3/js/d3.v3.min.js is in python3-mpld3 0.3git+20140910dfsg-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python3/dist-packages/mpld3/js/../../../../../share/javascript/d3/d3.min.js