问题描述

我(错误地?)在比较中使用了不是"并发现了这种奇怪的行为:

显然我应该使用:

但是由于小价值的测试用例，它工作了很长时间，直到我碰巧使用 495 的数字.

如果这是无效的语法，那为什么?难道我不应该至少得到警告吗?

"is" 不是检查值是否相等，而是检查两个变量是否指向同一对象实例.

ints 和 strings 对此会造成混淆，因为 is 和 == 可能恰好给出由于语言内部的工作方式，结果相同.

I (incorrectly?) used 'is not' in a comparison and found this curious behavior:

>>> a = 256
>>> b = int('256')
>>> c = 300
>>> d = int('300')
>>>
>>> a is not b
False
>>> c is not d
True

Obviously I should have used:

>>> a != b
False
>>> c != d
False

But it worked for a long time due to small-valued test-cases until I happened to use a number of 495.

If this is invalid syntax, then why? And shouldn't I at least get a warning?

"is" is not a check of equality of value, but a check that two variables point to the same instance of an object.

ints and strings are confusing for this as is and == can happen to give the same result due to how the internals of the language work.

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