code: def download(self, url, destination_path):
      
      self._pbar_url.update_total(1)
      future = self._executor.submit(self._sync_download, url, destination_path)
      return promise.Promise.resolve(future)
docs: Download url to given path.
  
      Returns Promise -> sha256 of downloaded file.
  
      Args:
        url: address of resource to download.
        destination_path: `str`, path to directory where to download the resource.
  
      Returns:
        Promise obj -> (`str`, int): (downloaded object checksum, size in bytes).