yum错误ImportError: No module named cElementTree的处理

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Determining fastest mirrors
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in 
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 285, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 136, in main
    result, resultmsgs = base.doCommands()
  File "/usr/share/yum-cli/cli.py", line 438, in doCommands
    return self.yum_cli_commands[self.basecmd].doCommand(self, self.basecmd, self.extcmds)
  File "/usr/share/yum-cli/yumcommands.py", line 698, in doCommand
    return base.search(extcmds)
  File "/usr/share/yum-cli/cli.py", line 1034, in search
    for (po, keys, matched_value) in matching:
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 2566, in searchGenerator
    for sack in self.pkgSack.sacks.values():
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 887, in 
    pkgSack = property(fget=lambda self: self._getSacks(),
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 669, in _getSacks
    self.repos.populateSack(which=repos)
  File "/usr/lib/python2.6/site-packages/yum/repos.py", line 308, in populateSack
    sack.populate(repo, mdtype, callback, cacheonly)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 165, in populate
    if self._check_db_version(repo, mydbtype):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 223, in _check_db_version
    return repo._check_db_version(mdtype)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1256, in _check_db_version
    repoXML = self.repoXML
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1455, in 
    repoXML = property(fget=lambda self: self._getRepoXML(),
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1447, in _getRepoXML
    self._loadRepoXML(text=self)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1437, in _loadRepoXML
    return self._groupLoadRepoXML(text, self._mdpolicy2mdtypes())
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1412, in _groupLoadRepoXML
    if self._commonLoadRepoXML(text):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1225, in _commonLoadRepoXML
    if self._latestRepoXML(local):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1194, in _latestRepoXML
    oxml = self._saveOldRepoXML(local)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1053, in _saveOldRepoXML
    xml = self._parseRepoXML(old_local, True)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1036, in _parseRepoXML
    return repoMDObject.RepoMD(self.id, local)
  File "/usr/lib/python2.6/site-packages/yum/repoMDObject.py", line 124, in __init__
    self.parse(srcfile)
  File "/usr/lib/python2.6/site-packages/yum/repoMDObject.py", line 140, in parse
    parser = iterparse(infile)
  File "/usr/lib/python2.6/site-packages/yum/misc.py", line 1141, in cElementTree_iterparse
    _cElementTree_import()
  File "/usr/lib/python2.6/site-packages/yum/misc.py", line 1136, in _cElementTree_import
    import cElementTree
ImportError: No module named cElementTree

报什么import cElementTree错误，查了半天，搞了半天这台上装了个oracle，环境变量被动了。
解决方法如下：

unset LD_LIBRARY_PATH