来自 sys.getrefcount 的意外结果

2022-01-16 00:00:00 python garbage-collection

问题描述

当我输入时:

>>> astrd = 123
>>> import sys
>>> sys.getrefcount(astrd)
3
>>>

我不知道 astrd 在哪里使用了 3 次?

I am not getting where is astrd used 3 times ?

解决方案

被引用3次的不是astrd，而是值123.astrd 只是(不可变)数字 123 的名称，可以多次引用.除此之外，通常共享小整数:

It's not astrd that is referenced three times, but the value 123. astrd is simply a name for the (immutable) number 123, which can be referenced however many times. Additionally to that, small integers are usually shared:

>>> astrd = 123 >>> sys.getrefcount(astrd) 4 >>> j = 123 >>> sys.getrefcount(astrd) 5

在第二个赋值中，没有创建新的整数，而是 j 只是整数 123 的新名称.

In the second assignment, no new integer is created, instead j is just a new name for the integer 123.

但是，给定非常大的整数，这不成立:

However, given very large integers, this does not hold:

>>> i = 823423442583 >>> sys.getrefcount(i) 2 >>> j = 823423442583 >>> sys.getrefcount(i) 2

共享整数是 CPython(以及其他)的一个实现细节.由于小整数经常被实例化，共享它们可以节省大量内存.这是因为整数是不可变的.

Shared integers are an implementation detail of CPython (among others). Since small integers are instantiated very often, sharing them saves a lot of memory. This is made possible by the fact that integers are immutable in the first place.

有关第二个示例中的附加参考，请参阅.codeape 的回答.

For the additional reference in the second example, cf. codeape's answer.

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