检查 False 的正确方法是什么?

2022-01-19 00:00:00 python boolean boolean-expression

问题描述

哪个更好?(为什么?)

Which is better? (and why?)

if somevalue == False:

if somevalue is False:

如果 somevalue 是字符串,你的答案会改变吗?

Does your answer change if somevalue is a string?


解决方案

这取决于 somevalue 可以是什么:如果 somevalue 可以是任何你可以检查它的东西一个布尔值和 not:

It rather depends on what somevalue can be: if somevalue could be anything you could check that it's a boolean and not:

if isinstance(somevalue, bool) and not somevalue

这不依赖于 False 是单例.如果它总是一个单例,你也可以这样做:

this doesn't rely on False being a singleton. If it always is a singleton you can also do:

if somevalue is False

<小时>

但是 Python 的 PEP8 声明你不应该关心它是否与类有关,只需使用:


But PEP8 of Python states you shouldn't care if it about the class and just use:

if not somevalue

这将评估 somevalue 是否为假".请参阅 关于真值测试的 Python 文档.

this will evaluate if somevalue is "falsy". See Python documentation on Truth value testing.

PEP8 状态:

不要使用 == 将布尔值与 True 或 False 进行比较.

Don't compare boolean values to True or False using == .

并给出这些例子:

Yes:   if greeting:
No:    if greeting == True:
Worse: if greeting is True:

在您的情况下翻译为:

Yes:   if not greeting:
No:    if greeting == False:
Worse: if greeting is False:

请记住,除了空字符串 '' 之外,每个字符串都被认为是真实的".

Keep in mind that each string is considered "truthy" except the empty string ''.

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