Since python 2 will be end of life. In Frankfurt release, we need to migrate to python3.

A couple of small changes are required to invoke python3 in some of the scripts.

Some docker files install python packages like pip; in alpine, pip is included with the python3 package itself, there's no separate py3-pip (cf. https://pkgs.alpinelinux.org/contents?branch=v3.8&name=python3&arch=x86_64&repo=main and https://pkgs.alpinelinux.org/packages?name=py3-pip&branch=v3.8)