yum-3.2.3-1.fc7 fails with the following exception traceback:

Running Transaction
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.main(sys.argv[1:])
  File "/usr/share/yum-cli/yummain.py", line 180, in main
    base.doTransaction()
  File "/usr/share/yum-cli/cli.py", line 382, in doTransaction
    self.runTransaction(cb=cb)
  File "/usr/lib/python2.5/site-packages/yum/__init__.py", line 571, in
runTransaction
    errors = self.ts.run(cb.callback, '')
  File "/usr/lib/python2.5/site-packages/yum/rpmtrans.py", line 251, in callback
    self._instProgress( bytes, total, h )
  File "/usr/lib/python2.5/site-packages/yum/rpmtrans.py", line 330, in
_instProgress
    self.complete_actions, self.total_actions)
  File "/usr/share/yum-cli/output.py", line 485, in event
    if self.output and (sys.stdout.isatty() or bytes == total):
NameError: global name 'bytes' is not defined

This only hits when sys.stdout.isatty() yields false, so running yum update from
a terminal, on an interactive ssh session, or even as ssh -t host yum update, it
works.  However ssh -t doesn't cut it when starting yum update on dozens of
machines in parallel.

I'm not entirely sure it does start messing with the rpm database before
crashing.  I've got some mess in the rpm databases of some affected machines,
but I can't tell whether the mess was already present before this error.