Python的不变性 [英] Immutability in Python

问题描述

我试图了解不变性如何在python中工作.由于字符串在python中是不可变的，因此我期望每次执行字符串操作时id都会更改，但它不能按预期工作. 例子: t上的最后一个操作不会更改其id.有什么想法吗?

I trying to understand how the immutability works in python. Since string are immutable in python, I was expecting the id to change every time I perform a string operation but it doesn't work as expected. example: The last operation on t doesn't change its id. Any ideas why?

推荐答案

我在不同的单元格[memory containing variables (I will not go to the bit level)]中有一排苹果，其中有些是空的[cells containing garbage / empty value].

I had a row of apples in different cells [memory containing variables (I will not go to the bit level)], of which some were empty [cells containing garbage / empty value].

我拿出一个.它在单元格3 [logical address = 3]中.

I took one out. It was in cell 3 [logical address = 3].

我将其涂成蓝色(在我使用未来的技术对其进行克隆以进行不变性演示之后).[committed an operation on it, same could go for addition for integers].

I painted it blue (after I cloned it using future tech, for immutability demonstration) [committed an operation on it, same could go for addition for integers].

我看了看它放在哪里，尽管第4单元是空闲的，但第3单元也是(因为这里不再有原始"苹果了)！所以我把它放回单元格3 [and although we get a "new" apple, it has the same address].

I looked where to put it, and although cell 4 was free, cell 3 was also (because the "original" apple is not here anymore)! So I put it back in cell 3 [and although we get a "new" apple, it has the same address].

t也一样(请注意，id是CPython中变量的内存地址)，但是由于我们在这里谈论的是苹果链"(字符串是由字符序列组成的，所以考虑必须要继续执行序列的空间量，因此，如果我的内存看起来像(_代表任意垃圾数据，'^'代表空间)

Same goes for your t (note that id is the memory address of the variable in CPython), but since we are talking about "chains of apples" here (strings are made of a characters sequence, we have to consider the amount of space we have to continue the sequence, so if I had my memory looking like (_ stands for arbitrary garbage data, '^' for space)

H e l l o _ _ _ _ _ B O O M
^ string pointer points here

，我想将字符串更改为"Hello you"，我可能会考虑使用可用空间:

and I wanted to change the string to "Hello you", I might consider using the free space:

H e l l o ^ y o u _ B O O M
^ string pointer points here

但是如果我想将字符串更改为"Hello world!"，我将不得不在其他地方寻找长度为"Hello world!"的可用空间(我们可能会在"BOOM"之后使用它，这很可能在垃圾回收中)收集的环境，看看您的ID有何不同):

But if I want to change the string to "Hello world!", I would have to look for free space in the length of "Hello world!" somewhere else (we might have it right after "BOOM", which is probable in a garbage collected environment, look at how your IDs differs):

H e l l o ^ y o u _ B O O M _ H e l l o ^ w o r l d ! _ G A R B A G E
                              ^ string pointer points here

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