torch.Tensor.item()方法的使用举例

在这里插入图片描述
原文及翻译:

item() → number
方法: item() 返回一个数
    Returns the value of this tensor as a standard Python number. 
    This only works for tensors with one element. For other cases, 
    see tolist().
    该方法的功能是以标准的Python数字的形式来返回这个张量的值.这个方法
    只能用于只包含一个元素的张量.对于其他的张量,请查看方法tolist().
    This operation is not differentiable.
    该操作是不可微分的,即不可求导.
    (译者注:返回的结果是普通Python数据类型,
    自然不能调用backward()方法来进行梯度的反向传播)

    Example:  例子:
    >>> x = torch.tensor([1.0])
    >>> x.item()
    1.0

代码实验展示:

Microsoft Windows [版本 10.0.18363.1316]
(c) 2019 Microsoft Corporation。保留所有权利。

C:\Users\chenxuqi>conda activate ssd4pytorch1_2_0

(ssd4pytorch1_2_0) C:\Users\chenxuqi>python
Python 3.7.7 (default, May  6 2020, 11:45:54) [MSC v.1916 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import torch
>>> torch.manual_seed(seed=20200910)
<torch._C.Generator object at 0x0000026F148DD330>
>>>
>>> x = torch.tensor([1.0])
>>> x.item()
1.0
>>> xt = x.item()
>>> xt
1.0
>>> type(xt)
<class 'float'>
>>> type(2.1)
<class 'float'>
>>>
>>> y = torch.tensor([1.0],requires_grad=True)
>>> y
tensor([1.], requires_grad=True)
>>> yt = y.item()
>>> yt
1.0
>>> type(yt)
<class 'float'>
>>> type(2.3)
<class 'float'>
>>>
>>>
>>>
>>>
>>>
>>> yt.backward()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'float' object has no attribute 'backward'
>>> xt.backward()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'float' object has no attribute 'backward'
>>>
>>>
>>>

代码实验展示:

Microsoft Windows [版本 10.0.18363.1316]
(c) 2019 Microsoft Corporation。保留所有权利。

C:\Users\chenxuqi>conda activate ssd4pytorch1_2_0

(ssd4pytorch1_2_0) C:\Users\chenxuqi>python
Python 3.7.7 (default, May  6 2020, 11:45:54) [MSC v.1916 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import torch
>>> x = torch.tensor([1])
>>> x.item()
1
>>> xt = x.item()
>>> xt
1
>>> type(xt)
<class 'int'>
>>> type(20200910)
<class 'int'>
>>> type(33)
<class 'int'>
>>>
>>>
>>>

代码实验展示:

Microsoft Windows [版本 10.0.18363.1316]
(c) 2019 Microsoft Corporation。保留所有权利。

C:\Users\chenxuqi>conda activate ssd4pytorch1_2_0

(ssd4pytorch1_2_0) C:\Users\chenxuqi>python
Python 3.7.7 (default, May  6 2020, 11:45:54) [MSC v.1916 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import torch
>>> torch.manual_seed(seed=20200910)
<torch._C.Generator object at 0x000001B54B7FD330>
>>>
>>> x = torch.randn(1)
>>> x
tensor([0.2824])
>>> x.item()
0.2823888957500458
>>> xt = x.item()
>>> xt
0.2823888957500458
>>>
>>> type(xt)
<class 'float'>
>>> type(1.2)
<class 'float'>
>>>
>>> y = torch.randn(3, 4)
>>> y
tensor([[-0.3715,  0.9088, -1.7601, -0.1806],
        [ 2.0937,  1.0406, -1.7651,  1.1216],
        [ 0.8440,  0.1783,  0.6859, -1.5942]])
>>>
>>>
>>> y.item()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: only one element tensors can be converted to Python scalars
>>>
>>>
>>>

torch.Tensor.item()方法的使用举例

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