“foo is None"和“foo is None"之间有什么区别吗?和“foo == None"?

问题描述

有什么区别:

如果 foo 是 None:通过

和

if foo == None: pass

我在大多数 Python 代码(以及我自己编写的代码)中看到的约定是前者，但我最近遇到使用后者的代码.None 是 NoneType 的一个实例(也是唯一的实例，IIRC)，所以它应该无关紧要，对吧?有没有可能发生的情况?

解决方案

is 如果比较同一个对象实例，总是返回 True

而 == 最终由 __eq__() 方法决定

即

>>> 类 Foo(对象):def __eq__(自我，其他):返回真>>> f = Foo()>>> f == 无真的>>> f 是无错误的

Is there any difference between:

if foo is None: pass

and

if foo == None: pass

The convention that I've seen in most Python code (and the code I myself write) is the former, but I recently came across code which uses the latter. None is an instance (and the only instance, IIRC) of NoneType, so it shouldn't matter, right? Are there any circumstances in which it might?

解决方案

is always returns True if it compares the same object instance

Whereas == is ultimately determined by the __eq__() method

i.e.

>>> class Foo(object):
       def __eq__(self, other):
           return True

>>> f = Foo()
>>> f == None
True
>>> f is None
False

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