[root@dev-mk tmp]# yum update --skip-broken
Loaded plugins: auto-update-debuginfo, fastestmirror, langpacks, merge-conf, presto, refresh-packagekit
Loading mirror speeds from cached hostfile
...
Setting up Update Process
Resolving Dependencies
--> Running transaction check
...
Install    2 Packages (+1 Dependent package)
Upgrade  178 Packages
Remove     1 Package

Total download size: 269 M
Is this ok [y/N]: y
Downloading Packages:
Setting up and reading Presto delta metadata
updates-testing/prestodelta                 | 514 kB     00:00     
Processing delta metadata
Traceback (most recent call last):
  File "/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 321, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 229, in main
    return_code = base.doTransaction()
  File "/usr/share/yum-cli/cli.py", line 547, in doTransaction
    problems = self.downloadPkgs(downloadpkgs, callback_total=self.download_callback_total_cb) 
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 2147, in downloadPkgs
    self.plugins.run('predownload', pkglist=pkglist)
  File "/usr/lib/python2.7/site-packages/yum/plugins.py", line 187, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/presto.py", line 633, in predownload_hook
    (problems, more) = downloadPkgs(conduit, pinfo, download_pkgs)
  File "/usr/lib/yum-plugins/presto.py", line 321, in downloadPkgs
    delta = getDelta(po, presto, conduit, conf_mp)
  File "/usr/lib/yum-plugins/presto.py", line 198, in getDelta
    conduit.info(5, -("Could not find delta rpm for package %s.%s.")
TypeError: bad operand type for unary -: 'str'

(and then it seems to hang and can't be interrupted by ctrl-C)

This is obviously a TypoError - it should have been '_' instead of '-'.

yum-3.4.3-18.fc17.noarch
yum-langpacks-0.2.4-3.fc17.noarch
yum-metadata-parser-1.1.4-6.fc17.i686
yum-plugin-auto-update-debug-info-1.1.31-4.fc17.noarch
yum-plugin-fastestmirror-1.1.31-4.fc17.noarch
yum-plugin-merge-conf-1.1.31-4.fc17.noarch
yum-presto-0.7.2-1.fc17.noarch
yum-utils-1.1.31-4.fc17.noarch