There are actually lots of implementations. The one I use is from Biopython.
http://bioinformatics.org/bradstuff/bp/api/Bio/Tools/KDTree/__init___KDTree.py.html In a message of Wed, 09 May 2007 11:53:13 +1000, Malcolm Ryan writes: >Does anyone know of a library which offers an efficient >implementation of kd-trees for python? I'm writing some flocking >code, so I want to be able to detect all objects within radius r of a >particular point. > >Malcolm >-- > "Progress should mean that we are always changing the world to fit > the vision, instead we are always changing the vision." > - G.K.Chesterton, Orthodoxy > >