检查 False 的正确方法是什么?
问题描述
哪个更好?(为什么?)
Which is better? (and why?)
if somevalue == False:
或
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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