将两个变量与Python中在一行中声明的“is”运算符进行比较

Question

根据Documentation：

The current implementation keeps an array of integer objects for all integers between -5 and 256, when you create an int in that range you actually just get back a reference to the existing object. So it should be possible to change the value of 1. I suspect the behaviour of Python in this case is undefined. :-)

所以以下行为是正常的。在

>>> a = 256
>>> b = 256
>>> a is b
True
>>> c = 257
>>> d = 257
>>> c is d
False

但是当我声明这样的两个变量时，我得到了真的-

^{pr2}$

我已经检查了e和f引用的对象的身份-

>>> id(e)
43054020
>>> id(f)
43054020

它们是一样的。在

我的问题是当我们用分号分隔来声明e和f时会发生什么？为什么它们引用同一个对象（尽管这些值超出了Python的整数对象数组的范围）？在

如果你能像对初学者那样解释它，那就更好了。在

Answer 1

根据Python Data model这是一个意外的行为，这是一个实现细节：

Types affect almost all aspects of object behavior. Even the importance of object identity is affected in some sense: for immutable types, operations that compute new values may actually return a reference to any existing object with the same type and value, while for mutable objects this is not allowed. E.g., after a = 1; b = 1, a and b may or may not refer to the same object with the value one, depending on the implementation, but after c = []; d = [], c and d are guaranteed to refer to two different, unique, newly created empty lists. (Note that c = d = [] assigns the same object to both c and d.)