Sorry, I did not check if there is an older update for python-etcd. FYI: The build system should not try to build it on ppc64 anymore, there has been an update to koji. But it should have been there 9 days ago as well. Could you please add karma to the other update to make it easier to fix the broken dep in Fedora 26 GA?
The python code of this update works, but the metadata is not correct, leading to dep issues in some cases. This is because of bug https://bugzilla.redhat.com/show_bug.cgi?id=1304355 - since this update contains only metadata changes iirc it is not useful to be pushed to stable afaics. If bug 1304355 is fixed, it will be a useful stable update. Another option would be to just hardly depend on python2-dnf until it can be ported to python3.
raphgro: You need to wait for the update to be pushed to testing and be available on your mirrors before your test command would work. Another option would be to download python-PyPDF2 from koji, install it and then try to install pdf-stapler. But you did not test this update with the command in https://bodhi.fedoraproject.org/updates/python-PyPDF2-1.25.1-10.fc24#comment-435550