In case someone runs into this comment and is interested in checking out the book, the book is called AIMA(Artificial Intelligence: A modern approach), and here is the relevant code.
Oh. I should have guessed "practical ai programming" was actually PAIP(Paradigms...). I haven't read PAIP, but have read AIMA, and the topic under discussion occurs in AIMA; so I assumed OP meant AIMA.
My bad for getting the name of the book wrong. I thought of it as PAIP for so long I forget what the actual name is :) Great book though, even for those not especially interested in AI or Lisp
I agree, and relevantly to this post it's a deep book on programming where algorithms and algorithm design do appear but aren't really central. They're an essential part of the toolbox but not the focus.
When I overhauled that code for the third edition, I messed up the A* search. I don't remember what the bug was offhand -- just saying, the OP is not the only one who has trouble sometimes.
http://aima-python.googlecode.com/svn/trunk/search.py
It's a long file though.