$ yum
Traceback (most recent call last):
  File "/usr/bin/yum", line 14, in ?
    import yummain
  File "/usr/share/yum-cli/yummain.py", line 25, in ?
    import cli
  File "/usr/share/yum-cli/cli.py", line 30, in ?
    import shell
  File "/usr/share/yum-cli/shell.py", line 22, in ?
    from yum.constants import *
ImportError: No module named constants