/usr/lib/python3/dist-packages/tornado/platform/ is in python3-tornado 4.5.3-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/python3/dist-packages/tornado/platform/__init__.py
/usr/lib/python3/dist-packages/tornado/platform/asyncio.py
/usr/lib/python3/dist-packages/tornado/platform/auto.py
/usr/lib/python3/dist-packages/tornado/platform/caresresolver.py
/usr/lib/python3/dist-packages/tornado/platform/common.py
/usr/lib/python3/dist-packages/tornado/platform/epoll.py
/usr/lib/python3/dist-packages/tornado/platform/interface.py
/usr/lib/python3/dist-packages/tornado/platform/kqueue.py
/usr/lib/python3/dist-packages/tornado/platform/posix.py
/usr/lib/python3/dist-packages/tornado/platform/select.py
/usr/lib/python3/dist-packages/tornado/platform/twisted.py
/usr/lib/python3/dist-packages/tornado/platform/windows.py