/usr/lib/python2.7/dist-packages/twisted/conch/mixin.py is in python-twisted-conch 1:11.1.0-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/twisted/conch/../../../../../share/pyshared/twisted/conch/mixin.py