torch.Tensor.get_device
Tensor.get_device() -> Device ordinal (Integer)
For CUDA tensors, this function returns the device ordinal of the
   GPU on which the tensor resides. For CPU tensors, this function
   returns -1.
Example:
  >>> x = torch.randn(3, 4, 5, device='cuda:0')
  >>> x.get_device()
  0
  >>> x.cpu().get_device()
  -1
