Just mentioning this module for completeness. This code by Bill Bumgarner includes a C extension to do what you want without looping throughout every object in existence.
The code for the function is quite straightforward. Every Python object is represented in C by a pointer to a PyObject struct. Because id(x) is just the memory address of this struct, we can retrieve the Python object just by treating x as a pointer to a PyObject, then calling Py_INCREF to tell the garbage collector that we're creating a new reference to the object.
static PyObject *
di_di(PyObject *self, PyObject *args)
{
PyObject *obj;
if (!PyArg_ParseTuple(args, "l:di", &obj))
return NULL;
Py_INCREF(obj);
return obj;
}
If the original object no longer exists then the result is undefined. It may crash, but it could also return a reference to a new object that's taken the location of the old one in memory.
