Preupgrade crash when resuming

UPDATE

Seth Vidal has a better solution. Rather than just catching the exception, you can prevent it by correcting the error in the code, as noted by Anonymous in the comments:

Patch from Seth Vidal:
https://bugzilla.redhat.com/show_bug.cgi?id=538118#c41

diff --git a/preupgrade/__init__.py b/preupgrade/__init__.py
index 2e82f1e..d79ec4b 100644
--- a/preupgrade/__init__.py
+++ b/preupgrade/__init__.py
@@ -325,7 +325,7 @@ class PreUpgrade(yum.YumBase):
rf = open(repofile,"w")
for repo in [self.instrepo] + self.repos.listEnabled():
# adapted from YumRepository.write()
- repo._grabfunc.opts.user_agent = __user_agent__
+ repo.grabfunc.opts.user_agent = __user_agent__
yc = yumConfigParser()
yc.add_section(repo.id)
for k,v in repo.iteritems():

So the problem is that it tried to use _grabfunc, which doesn't exist, instead of grabfunc. Yay.

I was trying to upgrade to Fedora 12 today via preupgrade but had to stop my upgrade session due to a network issue. When I tried to resume, as you're supposed to be able to do, it started getting the metadata again and then it suddenly crashed!

[root@localhost ~]# preupgrade
/usr/lib/python2.6/site-packages/yum/__init__.py:203: UserWarning: Use .preconf instead of passing args to _getConfig
  warnings.warn('Use .preconf instead of passing args to _getConfig')
Loaded plugins: blacklist, dellsysidplugin2, presto, refresh-packagekit,
              : whiteout
Detected in-progress upgrade to Fedora 12 (Constantine)
....
preupgrade-updates (mirrorlist) 
  url: https://mirrors.fedoraproject.org/metalink?repo=updates-released-f12&arch=i386
  now: https://mirrors.fedoraproject.org/metalink?repo=updates-released-f12&arch=i386
unknown metadata being downloaded: metalink
Traceback (most recent call last):
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 764, in 
    widgets = PreUpgradeGtk()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 376, in __init__
    self._do_main()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 259, in _do_main
    self.main_preupgrade()
  File "/usr/share/preupgrade/preupgrade-gtk.py", line 436, in main_preupgrade
    download_progressbar=self.dnlProgress)
  File "/usr/lib/python2.6/site-packages/preupgrade/__init__.py", line 130, in setup
    self.complete_repo_setup()
  File "/usr/lib/python2.6/site-packages/preupgrade/__init__.py", line 328, in complete_repo_setup
    repo._grabfunc.opts.user_agent = __user_agent__
AttributeError: 'NoneType' object has no attribute 'opts'

That's obnoxious. I didn't want to restart it, as I'd already downloaded over a hundred MB of files. So, as root I looked at the file tripping the AttributeError, /usr/lib/python2.6/site-packages/preupgrade/__init__.py, and decided to catch the error:

    repo._grabfunc.opts.user_agent = __user_agent__            

became

try:                                                            
    repo._grabfunc.opts.user_agent = __user_agent__             
except AttributeError:                                          
    print "Can't set user_agent, repo._grabfunc = NoneType :( "

I then ran it again, and this caught two exceptions, but allowed me to proceed with seemingly no loss of functionality. I am now happily downloading still more amazing amounts of MB. Hurrah!

Now to file a relevant bug if it doesn't already exist. The oft duplicated, already existent RH bug is 538118.