The python3-firehose (0.5-2.fc28) RPM requires both Python 2 and Python 3:
$ dnf --disablerepo=* --enablerepo=rawhide repoquery --requires python3-firehose | grep python
python(abi) = 3.6
This happened due to recently introduced shebangs mangling , and you might see the warnings in the build log:
> + /usr/lib/rpm/redhat/brp-mangle-shebangs
> *** WARNING: mangling shebang in ./usr/lib/python3.6/site-packages/firehose/parsers/gcc.py from #!/usr/bin/env python to #!/usr/bin/python2. This will become an ERROR, fix it manually!
> *** WARNING: mangling shebang in ./usr/lib/python3.6/site-packages/firehose/parsers/cppcheck.py from #!/usr/bin/env python to #!/usr/bin/python2. This will become an ERROR, fix it manually!
The executables contain `#!/usr/bin/env python` shebang, which is forbidden by the guidelines and is automatically mangled to `#!/usr/bin/python2` during build. Please fix the shebang to be `#!/usr/bin/python3` explicitly  or remove the executable bit from the above files if not needed.
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!
This bug appears to have been reported against 'rawhide' during the Fedora 28 development cycle.
Changing version to '28'.
I have created a PR that fixes the issue:
May I ask to review the PR and rebuild the package?
Built into rawhide as https://koji.fedoraproject.org/koji/taskinfo?taskID=25902226
Please, also Fedora 28.
Built for Fedora 28 ("f28-candidate") here:
python-firehose-0.5-3.fc28 has been pushed to the Fedora 28 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-2018-dc9b50f82f
python-firehose-0.5-3.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.