I’m just going on record to state that the two reasons I’ve seen on the net for lack of tree-based collections in the Python standard library — (1) that they have bad locality (gee, very unlike huge memory-hogging randomized hash tables, oh and just try scanning one of those…), and (2) that Python makes it so simple to write your own, just do that! (well, yes I can and have, but hey it’s 2011 already, rbtrees are like 40 years old!) — are inane.