Python-based Garbage Collection

garbage_collection.py

import gc
import ctypes

gc.set_debug(gc.DEBUG_SAVEALL)

class PyObject(ctypes.Structure):
    _fields_ = [("refcnt", ctypes.c_long)]

object1 = {}
object2 = {}
object3 = {}
object1['reference_to_2'] = object2
object2['reference_to_1'] = object1
object3['some_key'] = 1

object1_memory_address = id(object1)
object2_memory_address = id(object2)
object3_memory_address = id(object3)

print "Before garbage collection --->"
print "Refcount for object1: {count}".format(
  count=PyObject.from_address(object1_memory_address).refcnt
)
print "Refcount for object2: {count}".format(
  count=PyObject.from_address(object2_memory_address).refcnt
)
print "Refcount for object3: {count}".format(
  count=PyObject.from_address(object3_memory_address).refcnt
)

del object1, object2, object3
gc.collect()

print "After garbage collection --->"
print "Refcount for object1: {count}".format(
  count=PyObject.from_address(object1_memory_address).refcnt
)
print "Refcount for object2: {count}".format(
  count=PyObject.from_address(object2_memory_address).refcnt
)
print "Refcount for object3: {count}".format(
  count=PyObject.from_address(object3_memory_address).refcnt
)

print "Objects that cannot be cleaned up by reference counting: --->"
for x in gc.garbage:
  print x