Retrieving Object References from Variable IDs in Python

The id() function in Python returns the unique identity of an object. It is tempting to wonder if it is possible to reverse this process and obtain the object from its ID.

Specifically, we want to check if dereferencing the ID of a variable retrieves the original object:

dereference(id(a)) == a

Understanding the concept of dereferencing and its potentialability in Python is key when approaching this question.

Dereferencing in Python

Dereferencing involves retrieving the underlying object or value from a variable ID. Unfortunately, Python does not provide a native mechanism for dereferencing an ID directly.

Academic Approach

Despite the limitations of Python's built-in capabilities, it is possible to develop a utility function that simulates the inverse of the id() function. This function, di(), utilizes a combination of C-level APIs and type inference to retrieve the object reference from its ID:

import _ctypes

def di(obj_id):
    return _ctypes.PyObj_FromPtr(obj_id)

Example

Using the di() function, we can retrieve the original object from its ID:

a = 42
b = 'answer'
print(di(id(a)))  # -> 42
print(di(id(b)))  # -> answer

Caution

While this approach provides a theoretical understanding of dereferencing variable IDs in Python, it is important to note that the di() function should be used with caution due to potential memory safety and stability issues.