code: def get_thumbnails(self, *args, **kwargs):
          
          # First, delete any related thumbnails.
          source_cache = self.get_source_cache()
          if source_cache:
              thumbnail_storage_hash = utils.get_storage_hash(
                  self.thumbnail_storage)
              for thumbnail_cache in source_cache.thumbnails.all():
                  # Only iterate files which are stored using the current
                  # thumbnail storage.
                  if thumbnail_cache.storage_hash == thumbnail_storage_hash:
                      yield ThumbnailFile(name=thumbnail_cache.name,
                                          storage=self.thumbnail_storage)
docs: Return an iterator which returns ThumbnailFile instances.