Question

In CPython, the builtin-function id(x) returns the memory address of x.
Is it possible to reverse this ?

Something like object_by_memoryadress(id(x)) == x.

Update: The reason I need this is, because I’m using a program with embedded Python. And in this program I can create so called “Nodes” that can communicate with each other, but only with integers, strings, and stuff, but I’d need to “transfer” a list between them (which is not possible the usual way).

Answer 1

I have created a shared library that contains the following code:

#include "Python.h"
extern "C" __declspec(dllexport) PyObject* PyObjectFromAdress(long addr) {
    return (PyObject*) addr;
}

compiled it and wrapped it using ctypes:

import ctypes
dll = ctyes.cdll.thedll
object_from_id = dll.PyObjectFromAdress
object_from_id.restype = ctypes.py_object()

Now you can exchange python objects through their memory adress within one python process.

l1 = []
l2 = object_from_id( id(l1) )
print l1 == l2
l1.append(9)
print l2

But be aware of already garbage collected objects ! The following code will crash the Python interpreter.

l2 = object_from_id( id([]) )
l2.append(8)