Python“如果不是"语法 [英] Python 'If not' syntax

问题描述

我对如此多的 Python 开发人员如何/为什么在他们的条件语句中使用 if not 感到有些困惑.

I'm a bit confused about how/why so many python developers use if not in their conditional statements.

例如，假设我们有一个函数，

for example, lets say we had a function,

def foo(bar = None):
    if not bar:
        bar = 2

但是为什么要这样呢?我的意思是，if bar != None 或 if bar is not None 会不会更明确?if not 想说什么?

But why go about this way? I mean, wouldn't doing if bar != None or if bar is not Nonebe more explicit? What does if not try to say?

推荐答案

是的，if bar is not None 更明确，因此更好，假设它确实是您想要的.情况并非总是如此，存在细微差别:if not bar: 将在 bar 是任何类型的零或空容器或 False 时执行>.许多人确实使用 not bar，而他们确实使用意味着 bar is not None.

Yes, if bar is not None is more explicit, and thus better, assuming it is indeed what you want. That's not always the case, there are subtle differences: if not bar: will execute if bar is any kind of zero or empty container, or False. Many people do use not bar where they really do mean bar is not None.

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