/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/ is in libpython3.5-dbg 3.5.3-1+deb9u1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/Makefile
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/Setup
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/Setup.config
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/Setup.local
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/config.c
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/config.c.in
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/install-sh
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/libpython3.5.so
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/libpython3.5dm.a
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/libpython3.5dm.so
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/makesetup
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/python-config.py
/usr/lib/python3.5/config-3.5dm-x86_64-linux-gnu/python.o