code: def download(self, filename=None):
          
          tmp_file, f_suffix = download_file(self.url)
          if not filename is None:
              shutil.move(tmp_file, filename)
              return filename
          else:
              return tmp_file
docs: Download an attachment. The files are currently not cached since they
          can be overwritten on the server.
  
          Parameters
          ----------
          filename : string, optional
              Optional name for the file on local disk.
  
          Returns
          -------
          string
              Path to downloaded temporary file on disk