id(obj) returns an integer with object address in python (cPython). What about the reverse: return python object by address?

Method 1: using gc

The registry of (almost) all python objects is handled by the built-in garbage collector module gc. The list of objects can be retrieved using gc.get_objects(). We can find the needed object using a lookup dictionary.

import gc

def di(addr):
    return {id(i): i for i in gc.get_objects()}[addr]

x = ['hello world']

But not every object (and not at all times) can be accessed this way. For example, built-in immutable types such as strings, bytes, numbers, are not in the returned list.

Method 2: using ctypes

A faster way is to use ctypes which nicely casts arbitrary addresses into object and data types.

from ctypes import cast, py_object

def di(addr):
   return cast(addr, py_object).value

print(di(id("hello world")))

Note that, as many other functions in ctypes, cast does not check the validity of the input. If you pass an invalid pointer, you will likely crash the interpreter.