Para openSUSE Factory ejecute lo siguiente como root:
zypper addrepo https://download.opensuse.org/repositories/home:adrianSuSE/openSUSE_Factory/home:adrianSuSE.repo
zypper refresh
zypper install python-marshmallow
Para 15.7 ejecute lo siguiente como root:
zypper addrepo https://download.opensuse.org/repositories/home:adrianSuSE/15.7/home:adrianSuSE.repo
zypper refresh
zypper install python-marshmallow
Para 15.6 ejecute lo siguiente como root:
zypper addrepo https://download.opensuse.org/repositories/home:adrianSuSE/15.6/home:adrianSuSE.repo
zypper refresh
zypper install python-marshmallow