pytorch torch.device类（表示在其上或将要分配torch.Tensor的设备）

from https://pytorch.org/docs/1.1.0/tensor_attributes.html?highlight=torch%20device#torch.torch.device

CLASS torch.device

A torch.device is an object representing the device on which a torch.Tensor is or will be allocated.
torch.device是一个对象，表示在其上或将要分配torch.Tensor的设备。

The torch.device contains a device type (‘cpu’ or ‘cuda’) and optional device ordinal for the device type. If the device ordinal is not present, this represents the current device for the device type; e.g. a torch.Tensor constructed with device ‘cuda’ is equivalent to ‘cuda:X’ where X is the result of torch.cuda.current_device().
torch.device包含设备类型（“ cpu”或“ cuda”）和该设备类型的可选设备序号。
如果设备序号不存在，则代表设备类型的当前设备；
例如 用设备’cuda’构造的torch.Tensor等效于’cuda：X’，其中X是torch.cuda.current_device（）的结果。

A torch.Tensor’s device can be accessed via the Tensor.device property.
可以通过Tensor.device属性访问torch.Tensor的设备。

A torch.device can be constructed via a string or via a string and device ordinal
可以通过字符串或通过字符串和设备序号构造torch.device

Via a string:

>>> torch.device('cuda:0')
device(type='cuda', index=0)

>>> torch.device('cpu')
device(type='cpu')

>>> torch.device('cuda')  # current cuda device
device(type='cuda')

Via a string and device ordinal:

>>> torch.device('cuda', 0)
device(type='cuda', index=0)

>>> torch.device('cpu', 0)
device(type='cpu', index=0)

NOTE
The torch.device argument in functions can generally be substituted with a string. This allows for fast prototyping of code.
函数中的torch.device参数通常可以用字符串替换。
这样可以快速编写代码原型。

>>> # Example of a function that takes in a torch.device 带有torch.device的函数示例
>>> cuda1 = torch.device('cuda:1')
>>> torch.randn((2,3), device=cuda1)

>>> # You can substitute the torch.device with a string 您可以用字符串替换torch.device
>>> torch.randn((2,3), device='cuda:1')

NOTE

For legacy reasons, a device can be constructed via a single device ordinal, which is treated as a cuda device. This matches Tensor.get_device(), which returns an ordinal for cuda tensors and is not supported for cpu tensors.
出于遗留原因，可以通过单个设备序号（被视为cuda设备）构造设备。 
这与Tensor.get_device（）匹配，后者为cuda张量返回序数，而cpu张量不支持该序数。

>>> torch.device(1)
device(type='cuda', index=1)

NOTE

Methods which take a device will generally accept a (properly formatted) string or (legacy) integer device ordinal, i.e. the following are all equivalent:
使用设备的方法通常会接受（正确格式化的）字符串或（旧式）整数设备序数，即以下所有等效方法：

>>> torch.randn((2,3), device=torch.device('cuda:1'))
>>> torch.randn((2,3), device='cuda:1')
>>> torch.randn((2,3), device=1)  # legacy