It could make sense to add clean, working recipes to e.g. the functools documentation.  The cached_property in the wiki uses a TTL, other like Pyramid’s reify decorator make properties that ensure the fget function is called only once per instance, and there may be subtly different variants out there.  I don’t know if there’s a universally useful variant that should be added to the sdlib right now.  (I don’t think a C implementation is needed.)

On a related note, the Python docs about desciptors may be missing entry-level explanations, as described here: http://me.veekun.com/blog/2012/05/23/python-faq-descriptors/