For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:frispete:python/openSUSE_Tumbleweed/home:frispete:python.repo
zypper refresh
zypper install rrdtool
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:frispete:python/15.4/home:frispete:python.repo
zypper refresh
zypper install rrdtool
For 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:frispete:python/15.3/home:frispete:python.repo
zypper refresh
zypper install rrdtool