Get subprocess error output from shell command

[Gnarlodious]

I'm running a shell command like:
plutil -convert xml1 "~/Library/Preferences/iCab/iCab 4 Bookmarks"

Getting error:
~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied

How would I capture this error using a method of subprocess?

I read the doc at
http://docs.python.org/release/3.0.1/library/subprocess.html

but confess I don't understand it.

-- Gnarlie
http://Gnarlodious.com/