Debian 9 Stretch comes with two 2.7 and 3.5 python versions. If you have not installed any python package yet you can choose between both by simply installing an appropriate package:
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-change-default-python-version-on-debian-9-stretch-linux
Very helpful howto, thanks a lot!
i changed python version selectively on per user basis,
will the LOCAL python default to 2.X if i update the system later on? or will i still be using 3.X