We need to support building Samba with Python3 as distributions are removing support for Python2. Alexander is working on migrating to waf 2.0.8. https://gitlab.com/samba-team/devel/samba/tree/abbra-py3-master-waf This is a blocker for Samba 4.9rc1.
Is this building only, or building and running? An (ironic) build of samba --without-python is the only practical goal for 4.9, and even that will be hard work.
this is fixed and should have been closed since quite a while