yum does not work any more

What is wrong with my YUM ?

[erwin@philipp ~]$ sudo yum update yum
'import site' failed; use -v for traceback
Traceback (most recent call last):
  File "/usr/bin/yum", line 6, in ?
    import yummain
  File "/usr/share/yum-cli/yummain.py", line 18, in ?
    import os
  File "/usr/local/lib/python2.5/os.py", line 134
    from os.path import (curdir, pardir, sep, pathsep, defpath, extsep, 
altsep,
                        ^
SyntaxError: invalid syntax


Thanks for help
philipp