Python: how to create finalizer garbage

finalizer_garbage.py

import gc

class A():
    # For Python, finalizers means instance objects with __del__ methods.
    def __del__(self):
        pass

print gc.garbage
# []

# create a finalizer garbage: a
a = A()                     # refcnt: 1
a.reference_cycle = a       # refcnt: 2
del a                       # refcnt: 1 (become garbage)
# garbage collection doesnt work on `a` because of finalizer,
# so gc moves `a` to garbage list
gc.collect()                
print gc.garbage
# [<__main__.A instance at 0xb780560c>]

# Python programmers should take care not to create such things.
# The programmer has to deal with this if they insist on creating
# this type of structure.
del gc.garbage[:]