alternative to hardcoding system util paths

[Stephen Burke]

I'm writing a python script and I'm using aptitude and update-grub in
the script.  Currently I just use the abolute path to the bins ie.
/usr/bin/aptitude.  Ultimately I'd like to package it and distribute
it as a deb.  What's the recommended way to get these paths so they
will work on any user's machine?  Are there any environment vars that
I should use or a service of some kind?

Any help or pointing in the right direction would be appreciated or if
there is a better list to post this let me know.

Steve