np.isnan()== False，但是np.isnan()不是False [英] np.isnan() == False, but np.isnan() is not False

问题描述

据我了解，==检查值的相等性，而is检查值背后的结构的身份(例如，其他语言中的===).

As far as I understand it, == checks for equality of value, and is checks for identity of structure behind value (as, say === in some other languages).

鉴于此，我不理解以下内容:

Given that, I don't understand the following:

np.isnan(30) == False
Out[19]: 
True
np.isnan(30) is False
Out[20]: 
False

其他身份检查似乎并非如此:

It appears not to be the case with other identity checks:

(5 == 4) == False
Out[22]: 
True
(5 == 4) is False
Out[23]: 
True

似乎np.isnan()返回False作为值而不是作为标识.为什么会这样呢?

It appears as if np.isnan() returns False as a value, but not as identity. Why is that the case?

推荐答案

numpy.isnan()返回兼容类型的对象:

>>> import numpy
>>> type(numpy.isnan(0))
<class 'numpy.bool_'>

这是一个自定义布尔值，可以有效地存储在numpy数组中，请参见

This is a custom boolean that can be stored efficiently in numpy arrays, see Numpy's Data Types documentation. The numpy.isnan() function can also operate on arrays, producing another array with results:

>>> numpy.isnan(numpy.array([1, 2]))
array([False, False], dtype=bool)

其中dtype还是Numpy布尔对象.

where again the dtype is the Numpy boolean object.

Python不能保证布尔操作必须始终返回单例布尔值.无论如何，您绝不应该测试is True或is False .直接在布尔运算中使用numpy.isnan()输出，使用not测试错误值:

Python makes no guarantees that boolean operations must always return a singleton boolean value. You should never test for is True or is False anyway. Use numpy.isnan() output directly in boolean operations, use not to test for false values:

if numpy.isnan(foo):

和

if not numpy.isnan(bar):

这篇关于np.isnan()== False，但是np.isnan()不是False的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！