Prompt for incomplete command

[Peng Yu]

Hi,

I used to remember if I type an incomplete command, I should see an
useful output such as which package I should install or what other
commands may be relevant to the incomplete command.

~$ hg
The program 'hg' is currently not installed.  You can install it by typing:
sudo apt-get install mercurial

But now I get the following error. It seems that there is some problem
with the python packages. But I don't think that I have changed
anything relevant in my system. Does anybody know what the problem
might be and how to fix this problem?

~$  hg
Traceback (most recent call last):
  File "/usr/lib/command-not-found", line 17, in <module>
    from CommandNotFound.util import crash_guard
ImportError: No module named CommandNotFound.util

-- 
Regards,
Peng