找不到"六",但它已经安装好了

我已six安装(甚至重新安装).

$ pip show six
---
Name: six
Version: 1.7.3
Location: /usr/lib/python2.6/site-packages
Requires: 

但是当我试图跑步时csvcut,它找不到它.

$ csvcut -n monster.csv
Traceback (most recent call last):
  File "/usr/bin/csvcut", line 5, in 
    from pkg_resources import load_entry_point
  File "/usr/lib/python2.6/site-packages/pkg_resources.py", line 2655, in 
    working_set.require(__requires__)
  File "/usr/lib/python2.6/site-packages/pkg_resources.py", line 648, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.6/site-packages/pkg_resources.py", line 546, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: six>=1.6.1

这是相关的但是csvcut:

#!/usr/bin/python
# EASY-INSTALL-ENTRY-SCRIPT: 'csvkit==0.8.0','console_scripts','csvcut'
__requires__ = 'csvkit==0.8.0'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('csvkit==0.8.0', 'console_scripts', 'csvcut')()
    )

这是在CentOS上.