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"

id is not a string encoding function. It returns a unique ID for the passed object, which may change between runs. — Colonel Thirty Two
– Colonel Thirty Two, Commented Jul 18, 2014 at 0:52

Community · Accepted Answer · 2017-05-23 11:53:04Z

19

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, 2017 at 11:53

CommunityBot

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answered Jul 18, 2014 at 1:00

Victor Castillo Torres

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3 Comments

dano Over a year ago

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.

Victor Castillo Torres Over a year ago

@dano I think so too but he answered Is there a reverse or inverse of the id built-in function?

dano Over a year ago

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.

Community · Accepted Answer · 2017-05-23 11:45:39Z

1

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.

edited May 23, 2017 at 11:45

CommunityBot

11 silver badge

answered Jul 18, 2014 at 0:53

dano

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