code: def kids(self):
          
          self._uptodate()
          return [key.kid for key in self._keys if key.kid != ""]
docs: Return a list of key IDs. Note that this list may be shorter then
          the list of keys. The reason might be that there are some keys with
          no key ID.
          
          :return: A list of all the key IDs that exists in this bundle