'not ==' 和 '!= (没有 is) 之间是否存在逻辑差异 [英] Is there a logical difference between 'not ==' and '!= (without is)

问题描述

Python 3.x 之间是否存在实质性差异:

Is there a substantial difference in Python 3.x between:

for each_line in data_file:
    if each_line.find(":") != -1:
        #placeholder for code
        #more placeholder

和

for each_line in data:
    if not each_line.find(":") == -1:
        #placeholder for code
        #more placeholder

我的问题不是针对上述用法，而是更普遍或更重要的问题 - 即使结果相同，这种语法差异是否以不同的方式起作用?逻辑上有区别吗?是否有更合适的任务，或者这仅仅是风格上的差异?如果这仅仅是风格，Python 程序员认为哪个更简洁?

My question isn't particular to the above usage, but is more general or essential - is this syntactical difference working in a different way, even though the result is the same? Is there a logical difference? Are there tasks where one is more appropriate or is this solely a stylistic difference? If this is merely stylistic, which one is considered cleaner by Python programmers?

另外，上面是问is和==有什么区别的反例吗?前者和后者一样，是对象身份和对象值相等的区别吗?我的意思是，在我上面的例子中，使用 not 时的 is 是隐式的吗?

Also, is the above an opposite instance of asking what the difference is between is and ==? Is the former, like the latter, a difference of object identity and object value equality? What I mean is, in my above example, is the is in using not implicit?

推荐答案

据我所知，在功能上它们并不完全相同；如果您正在与类进行比较，则该类可能有一个成员函数，__ne__ 在使用比较运算符 != 时调用，而不是 __eq__ 时调用使用比较==

As I understand it, functionally they are not entirely the same; if you are comparing against a class, the class could have a member function, __ne__ which is called when using the comparison operator !=, as opposed to __eq__ which is called when using the comparison ==

所以，在这种情况下，
not (a == b) 会在 a 上调​​用 __eq__，以 b 作为参数，然后 not 结果
(a != b) 会在 a 上调​​用 __ne__，以 b 作为参数.

So, in this instance,
not (a == b) would call __eq__ on a, with b as the argument, then not the result
(a != b) would call __ne__ on a, with b as the argument.

我会使用第一种方法(使用 !=)进行比较

I would use the first method (using !=) for comparison

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