I hate necrobumping but maybe this will help someone with the same issue.
Version 3.10 of urlgrabber resolves the error without having to modify any of the code itself.
First remove the old version of urlgrabber to prevent any issues:
pip uninstall urlgrabber
Unfortunately the latest version available on pip is 3.9.1 so you're going to need to pull the latest code from the git repo and compile it yourself.
git clone git://yum.baseurl.org/urlgrabber.git
cd urlgrabber && python setup.py install
You should now be on the latest version of urlgrabber. You can double check by running:
pip show urlgrabber
You should see version 3.10.x.
Yum should now be working again.