the final stage of packaging, the brp-python-bytecompiler is trying to compile a bunch of python3 code against the default /usr/bin/python which is python2 on CentOS7. Causing a flurry of errors. I've bypassed it by adding;

%global _os_install_post %(echo '%{_os_install_post}' | sed -e 's!/usr/lib[^[:space:]]/brp-python-bytecompile[[:space:]].$!!g')

as an added RPM_SPEC.

Info can be found here:
https://www.math-linux.com/linux/rpm/article/how-to-turn-off-avoid-brp-python-bytecompile-script-in-a-spec-file
https://pagure.io/packaging-committee/issue/755