Python inverse function of id(...) built-in function

Question

Is there a reverse or inverse of the id built-in function? I was thinking of using it to encode and decode string without taking too much time or having a lot of overhead like the PyCrypto library. The need for me is quite simple so I don't want to use PyCrypto for a simple encode and decode.

Something like:

>>> id("foobar")
4330174256
>>> reverse_id(4330174256) # some function like this to reverse.
"foobar"

[`base64`](https://docs.python.org/2/library/base64.html) might fit your needs better... — dano, Jul 18 '14 at 00:51
`id` is not a string encoding function. It returns a unique ID for the passed object, which may change between runs. — Colonel Thirty Two, Jul 18 '14 at 00:52

score 17 · Accepted Answer · edited May 23 '17 at 11:53

17

I do not wanna to steal the credits from the man who answered the question

This can be done easily by ctypes:

import ctypes
a = "hello world"
print ctypes.cast(id(a), ctypes.py_object).value
output:

hello world

edited May 23 '17 at 11:53

Community

1
1

answered Jul 18 '14 at 01:00

Victor Castillo Torres

10,581
7
40
50

Ah, cool! I guess I didn't scroll far enough down the page. I still think `base64` is much more appropriate for what the OP is trying to do here, though. – dano Jul 18 '14 at 01:06
1

@dano I think so too but he answered **Is there a reverse or inverse of the id built-in function?** – Victor Castillo Torres Jul 18 '14 at 01:07
Oh, for sure (which is why I upvoted you). But sometimes the OP thinks they needs an answer for one question, when they really need a different answer to a different question. – dano Jul 18 '14 at 01:12

score 1 · Answer 2 · edited May 23 '17 at 11:45

I think the base64 module would fit your needs here, rather than trying to use id:

>>> import base64
>>> base64.b64encode("foobar")
'Zm9vYmFy'
>>> base64.b64decode('Zm9vYmFy')
'foobar'

The answer to your literal question (can I look up an object by its id?) is answered here. ~~The short answer is no, you can't.~~ Edit: Victor Castillo Torres ponits out that this actually is possible if you're using CPython, via the ctypes module.

Python inverse function of id(...) built-in function

2 Answers2

Linked