This has been percolating for a while -- it just took a while to extract it from the guts of the larger project from whence it springs.
So I'm happy to announce the first public release of PyRtree, a pure python spatial index. It is quite bare bones, and alpha quality, at the moment, but has proven very useful to me nonetheless.
It isn't as speedy as the Rtree library, which links to a C library, but it has the benefits of simplicity, code flexibility, and ease of use: no compilation or library version headaches!
For those who haven't worked with this corner of computer science before, expect a post in the next week (or three) explaining what an R-Tree is and how to use it.