Given an adress, how can I access the object in Python?

February 16, 2023

How can I access a Python object by it’s address that I get from id(self.__dict__)?

The background is the following, I want to access one class instance from the other (both classes mimic custom dictionaries):

class1:
    def __init__(self):
        self.a =  class2(self)
        # I also tried self.a = class2(self.__dict__) which also does not seem to be a good idea

class2:
    def __init__(self, parentobject):
        self.parentobject = parentobject

As both class implement dictionaries, I can’t iterate over them due to infinite self-referencing

One way to get it working, I thought, would to pass and save only the address of the "parent" class instance.
But in order to access it, I would need to transform somehow the address into something I can access.

>Solution :

This is a way to do what you’re asking, but I’m not sure this works on just any implementation of Python besides the standard CPython, which uses the memory address of objects as their id. That’s an implementation detail entirely specific to CPython though. As for whether you should even be trying to do this, I’m not here to judge that:

import ctypes

# create an object
a = [1, 2, 3]

# get the id of the object
b = id(a)

# access the object by its id
c = ctypes.cast(b, ctypes.py_object).value

# print the object
print(c)  # output: [1, 2, 3]