code: def get_disk_cache(self, key=None):
          
          key = self.model.hash if key is None else key
          if not getattr(self, 'disk_cache_location', False):
              self.init_disk_cache()
          disk_cache = shelve.open(self.disk_cache_location)
          self._results = disk_cache.get(key)
          disk_cache.close()
          return self._results
docs: Return result in disk cache for key 'key' or None if not found.