def cache(self):
      """Caches the result of loader(filename) to cachename."""
      msg = 'Saving updates from more recent "%s" to "%s"'
      log.info(msg, self.filename, self.cachename)
      with open(self.cachename, 'wb') as output:
          cPickle.dump(self._dict, output, -1)
Caches the result of loader(filename) to cachename.