How to determine an ID on Python?

Question

I heard that the same strings have the same IDs like below:

>>>list1=[1,2,'aaa','bbb']
>>>list2=[3,4,'aaa','bbb']
>>>id(list1[2])
12345
>>>id(list2[2])
12345

but the following case does not hold the rule:

>>>list1=[1,2,'Hello World','bbb']
>>>list2=[3,4,'Hello World','bbb']
>>>id(list1[2])
12345
>>>id(list2[2])
12367

How are they different from each other?

Added

Python 2.7.5 (default, Mar  9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> list1 = [1, 2, 'aaa', 'bbb']
>>> list2 = [2, 3, 'aaa', 'bbb']
>>> id(list1[2])
4511557072
>>> id(list2[2])
4511557072
>>> list3 = [1, 2, 'Hello World', 'bbb']
>>> list4 = [2, 3, 'Hello World', 'bbb']
>>> id(list3[2])
4511542272
>>> id(list4[2])
4511542368

This almost never matters with immutable objects like strings. What do you need the strings' IDs for? — user2357112, Mar 31 '15 at 05:25
Also, when posting interpreter session transcripts, please copy-paste from an actual interpreter session rather than making up output. Made-up output is frequently wrong in crucial ways. — user2357112, Mar 31 '15 at 05:29
Please show a reproducible example. As @Marcin stated, your second snippet does not execute. — Amadan, Mar 31 '15 at 05:29
You might have the wrong concept about `id` there. It points to a memory location at which the String is stored. See: http://stackoverflow.com/questions/2123925/when-does-python-allocate-new-memory-for-identical-strings or http://stackoverflow.com/questions/24245324/about-the-changing-id-of-a-python-immutable-string — Calon, Mar 31 '15 at 05:29

score 2 · Accepted Answer · edited May 23 '17 at 12:14

2

Possible reason is that in your second example you use id(lst2[2]) instead of id(list2[2]). But in general I think, its up to python's interpreter to decide whether string objects containing the same string are actually the same string objects or not.

In addition this link has a bit of discussion and answers related to this question.

edited May 23 '17 at 12:14

Community

1
1

answered Mar 31 '15 at 05:20

Marcin

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nope this is not the answer. – A.J. Uppal Mar 31 '15 at 05:23
@A.J. I updated the answer. But if my answer is not correct, that which one is the correct one? – Marcin Mar 31 '15 at 05:25
Now that is the question :) – A.J. Uppal Mar 31 '15 at 05:26
@A.J. So please feel to provide the correct answer. – Marcin Mar 31 '15 at 05:28
The link is worth the upvote. Indeed, it's about autointerning of short strings. – Amadan Mar 31 '15 at 05:36

score -2 · Answer 2 · answered Mar 31 '15 at 05:25

-2

Your assumption of same string having the same id is right.

Could you give more details about your code? This is what I have got:

>>> list2=[3,4,'aaa','bbb']
>>> list1=[1,2,'aaa','bbb']
>>> list2=[3,4,'aaa','bbb']
>>> id(list1[2])
4449536920
>>> id(list2[2])
4449536920

answered Mar 31 '15 at 05:25

Da Tong

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'aaa' case returns same IDs. but 'Hello world' case does not. – Arena Son Mar 31 '15 at 05:28
It has a space. Check it in python interpreter. id(" ") is a constant through out. But id(" ") (two spaces) changes – Arundas R Mar 31 '15 at 05:32

How to determine an ID on Python?

Added

2 Answers2