Installing MATE on top of a GNOME system pulls in the deprecated pygtk2 bindings, due to the following in mate-desktop.spec: Requires: pygtk2 I'm not sure from what this is a remnant, but with the port to GTK+3 this certainly can't be correct.
[root@f25-origin rave]# repoquery --whatrequires pygtk2 <cut> caja-terminal-0:0.9.1-1.fc25.x86_64 <cut> exaile-0:3.4.5-2.fc24.noarch <cut> gajim-0:0.16.6-1.fc25.noarch gajim-0:0.16.7-1.fc25.noarch <cut> mate-desktop-0:1.16.1-1.fc25.x86_64 mate-desktop-0:1.16.1-3.fc25.x86_64 <cut> mintmenu-0:5.6.5-4.fc24.noarch <cut> pluma-0:1.16.0-1.fc25.i686 pluma-0:1.16.0-1.fc25.x86_64 pluma-beesu-plugin-0:0.4-27.fc24.x86_64 <cut> system-config-firewall-0:1.2.29-12.fc21.noarch system-config-firewall-0:1.2.29-15.fc25.noarch system-config-users-0:1.3.8-2.fc24.noarch <cut> Well i can add this to my TODO list and fix that for Mate packages with next builds, but as other package used by Mate desktop use it too. ... not in my hand. Curious why mate-desktop is listed here.
http://pkgs.fedoraproject.org/cgit/rpms/mate-desktop.git/diff/mate-desktop.spec?h=f19&id=11d67ce2b7c49c3fabb77f6ed148512ce12e20bb The requires is there since the first commit in repo. So this is a remnant from former gnome-desktop package.
mate-desktop-1.18.0-3.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-06e86bd44e
mate-desktop-1.18.0-3.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-06e86bd44e
mate-desktop-1.18.0-3.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.