weak-ref-eg-3.py

import ctypes
import weakref
import gc

class Serval: 
    def __init__(self, name, cousin = None):
        self.name = name
        self.cousin = cousin

class Cat:
    def __init__(self, name, cousin=None):
        self.name = name 
        self.cousin = cousin

servy = Serval("Servy")
whiky = Cat("Whiky", weakref.ref(servy))
# servy.cousin = whiky
servy.cousin = weakref.ref(whiky)

print(f"servy's refcount: {ctypes.c_long.from_address(id(servy)).value}")
print(f"whiky's refcount: {ctypes.c_long.from_address(id(whiky)).value}")

del servy
gc.collect()
print("AFTER DELETION OF servy")
print(f"whiky's refcount: {ctypes.c_long.from_address(id(whiky)).value}")

print(f"whiky's cousin: {whiky.cousin()}")