/usr/libexec/platform-python -c 'import dnf, json; db = dnf.dnf.Base(); print(json.dumps(db.conf.substitutions, indent=2))'
python -c 'import yum, pprint; yb = yum.YumBase(); pprint.pprint(yb.conf.yumvar, width=1)'
# yum install centos-release-scl-rh
# yum install devtoolset-9
$ scl enable devtoolset-9 bash