code: def _transfer_result(fut1, fut2):
    
    exc = fut1.get_exception()
    if exc is not None:
      tb = fut1.get_traceback()
      fut2.set_exception(exc, tb)
    else:
      val = fut1.get_result()
      fut2.set_result(val)
docs: Helper to transfer result or errors from one Future to another.