RuntimeError: element 0 of tensors does not require grad and does not have a grad_fnException ignor

       在pytorch代码进行loss.backward的时候出现下面报错：

RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn
Exception ignored in: <function tqdm.__del__ at 0x000001EF82E38EA0>

        原因是在pytorch对Tensor进行backward自动求导时，代码中的

loss.requires_grad 设置为了 False

        因此我们只需要在代码中加入：

loss.requires_grad = True