Looks extensive and I'll likely try using the module at some point.

One thing, why not stash all the function methods under a "ring" or "cache" attribute, eg

  @ring.lru()
  def foo()
    ..

  foo.cache.update()
  foo.cache.delete() 
  ..

This might be less likely to clash with any existing function attributes (if you're wrapping a 3rd party function say).