import struct

_builtin_id = id
_ptr_max    = 256 ** struct.calcsize("P")


class id(long):
    """Replacement for the built-in id() function.

Instances of 'id' keep a reference to the original object, to prevent
the memory address from becoming meaningless.  The object is available
in the public 'obj' attribute.  Additionally, this id() never produces
negative numbers.
"""

    def __new__(cls, obj):
        my_id = _builtin_id(obj) % _ptr_max
        result = super(id, cls).__new__(cls, my_id)
        result.obj = obj
        return result

    def __repr__(self):
        return "<id 0x%x of '%s' object>" % (self, type(self.obj).__name__)