为什么两个单独创建的不可变对象具有相同的id，而可变对象却具有不同的含义，而它们都引用相同的值? [英] Why two individually created immutable objects have same id and mutable objects have different while both refer to same values?

问题描述

两个单独创建的可变列表具有不同的ID.

Two individually created mutable list have different ids.

Python SHELL :(可变)

>>> mylist = ['spam', 'eggs']
>>> yourlist = ['spam', 'eggs']
>>> id(mylist), id(yourlist)
(49624456, 48910408)

两个单独创建的不可变字符串具有相似的ID.

While two individually created immutable strings have similar ids.

Python SHELL :(不可变)

>>> a = 10
>>> b = 10
>>> id(a), id(b)
(507099072, 507099072)

a和b是否引用同一对象?如果没有，为什么ID相似? mylist和yourlist是否引用了不同的对象?如果是，为什么它们具有不同的ID.

Is a and b referencing to a same object? If no, why ids are similar? Is mylist and yourlist referencing to different objects? If yes, why they have different ids.

推荐答案

Python会缓存一些小的字符串和数字:

Python caches some small strings and numbers: http://docs.python.org/2/c-api/int.html#PyInt_FromLong

当前实现为所有对象保留一个整数对象数组 在-5到256之间的整数，当您在该范围内创建int时， 实际上只是获取对现有对象的引用.

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.

id(some_list)始终为您提供容器的地址-内存中列出对象，而不是列表中的字符串！

And id(some_list) always gives you the address of container - list object in memory, not strings in list!

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