Ben, Perhaps try communicating the problem you're trying to solve with the data structure. ie, what you're storing, what would you be looking for when searching stored objects... This would yield better advice, and share information within the context of sugar. James. <div class="gmail_quote">2009/6/8 Benjamin M. Schwartz <<a href="mailto:bmschwar@fas.harvard.edu">bmschwar@fas.harvard.edu</a>> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> I've had amazing difficulty communicating what I'm looking for here. Those closest thing is <a href="http://en.wikipedia.org/wiki/Rope_%28computer_science%29" target="_blank">http://en.wikipedia.org/wiki/Rope_(computer_science)</a> A rope is a binary tree that _imposes_ an ordering on its leaves that has nothing whatsoever to do with their values (the values are essentially opaque). This is very unusual; almost all standard tree structures _derive_ an ordering _from_ the values. Unfortunately, all implementations of Ropes that I have seen so far are designed only to store Chars, whereas I need to store arbitrary python objects. I'd like to avoid coding such a beast myself, but I may have no choice. It would help if someone could identify Ropes as a specialization of a more general type of tree, but I have not seen any claims of this kind. The only property I'm looking for that Ropes don't intrinsically satisfy is "Reverse lookup". That is to say, I would like to be able to hold a pointer to a particular object in the tree, and at some later time, walk back up the tree from that pointer to work out the object's current index. It does seem like that should be doable with a Rope, especially if we move to the special case in which the leaves are "arrays of length 1". --Ben _______________________________________________ Sugar-devel mailing list <a href="mailto:Sugar-devel@lists.sugarlabs.org">Sugar-devel@lists.sugarlabs.org</a> <a href="http://lists.sugarlabs.org/listinfo/sugar-devel" target="_blank">http://lists.sugarlabs.org/listinfo/sugar-devel</a> </blockquote></div>