UserWarning: The given NumPy array is not writable, and PyTorch does not support non-writable tenso

UserWarning: The given NumPy array is not writable, and PyTorch does not support non-writable tensors.

修改方式：

Instead of using 
img = transforms.ToTensor()(img)

Use this:
img = transforms.ToTensor()(np.array(img))

ToTensor()接收 PIL 对象或 numpy 数组。因此，将 pil 数组显式更改为 numpy 数组就可以了。