Here's a utility function based on a (now-deleted) comment made by "Tiran" in a weblog discussion @Hophat Abc references in his own answer that will work in both Python 2 and 3.

Disclaimer: If you read the the linked discussion, you'll find that some folks think this is so unsafe that it should never be used (as likewise mentioned in some of the comments below). I don't agree with that assessment but feel I should at least mention that there's some debate about using it.

import _ctypes

def di(obj_id):
    """ Inverse of id() function. """
    return _ctypes.PyObj_FromPtr(obj_id)

if __name__ == '__main__':
    a = 42
    b = 'answer'
    print(di(id(a)))  # -> 42
    print(di(id(b)))  # -> answer

To simplify, when you do b = deepcopy(a), that means that nested dictionaries in b are not identical to the nested dictionaries in a, but it doesn't break the internal structure. Dictionaries accessible via different keys are still identical, and cyclical dictionaries (for example a[some_key] is a) remain cyclical.

The best way to deal with this is to make sure your dictionary doesn't have any unwanted shared references in the first place, for example by doing:

    return {
        "main_key": {
            "x": d2,
            "y": deepcopy(d2),
        }
    }

But if you don't control the way the data arrives, you could use a recursive function like this one:

def copy_tree(original):
    '''Creates a deep copy of a dictionary, but the copy will
    be a tree, so no shared references. Cyclic dictionaries will
    cause a recursion error.
    All keys, and all non-dictionary values are not copied but used
    as-is.'''
    if isinstance(original, dict):
        return {key: copy_tree(value) for key, value in original.items()}
    return original

ctypes.cast.

>>> import ctypes
>>> c_long_p = ctypes.POINTER(ctypes.c_long)
>>> some_long = ctypes.c_long(42)
>>> ctypes.addressof(some_long)
4300833936
>>> ctypes.cast(4300833936, c_long_p)
<__main__.LP_c_long object at 0x1005983b0>
>>> ctypes.cast(4300833936, c_long_p).contents
c_long(42)