How do circular references between objects with __del__ methods behave differently in Python 3.4+ compared to earlier versions?

Before Python 3.4 (PEP 442), objects in a reference cycle where any participant defined __del__ could never be automatically collected -- they were placed in gc.garbage and effectively leaked forever, requiring manual intervention. Since PEP 442, the garbage collector can safely finalize objects in cycles even with __del__ methods present, calling each object's __del__ exactly once and correctly handling resurrection edge cases, though relying on __del__ for critical logic is still discouraged.

import gc

class Node:
    def __del__(self):
        print('Node destroyed')

a, b = Node(), Node()
a.ref, b.ref = b, a  # cycle
del a, b
gc.collect()  # in 3.4+, both __del__ methods run correctly during collection