The python3-backcall RPM requires both Python 2 and Python 3:

$ dnf repoquery --repo=rawhide --requires python3-backcall
python(abi)
python(abi) = 3.7

Except in very special circumstances, there is no need for one package
to drag in both Python stacks. Usually, this is a packaging error.

Please split your package, or remove the stray dependencies.

It's ok to do this in Rawhide only, however, it would be greatly
appreciated if you could push it to Fedora 28 as well.


If anything is unclear, or if you need any kind of assistance, you can
ask on IRC (#fedora-python on Freenode), or reply here. We'll be happy
to help investigating or fixing this issue!