import gc
import _testcapi
import os
import ctypes

lib = ctypes.pythonapi

PyObject_GC_Track = lib.PyObject_GC_Track
PyObject_GC_Track.argtypes = (ctypes.py_object,)
PyObject_GC_Track.restype = None

PyObject_GC_UnTrack = lib.PyObject_GC_UnTrack
PyObject_GC_UnTrack.argtypes = (ctypes.py_object,)
PyObject_GC_UnTrack.restype = None

def PyGC_retrack(obj):
    PyObject_GC_UnTrack(obj)
    PyObject_GC_Track(obj)

class Namespace:
    pass

def func():
    # Strong references:
    #   remove <-> ns
    # and
    #   ns -> obj -> remove

    ns = Namespace()

    obj = _testcapi.BadGC2Type()

    def remove(arg):
        # create a closure to keep obj alive
        x = ns
        return "must never be called"

    remove.__name__ = "evil_func"
    assert remove.__closure__[0].cell_contents is ns

    obj.set_func(remove)

    ns.obj = obj
    ns.remove = remove

    # reorder objects in GC collection generation 0
    PyGC_retrack(remove)
    PyGC_retrack(remove.__closure__[0])
    PyGC_retrack(ns)
    PyGC_retrack(ns.__dict__)
    PyGC_retrack(obj)

    if 0:
        # dump some info
        for obj in gc.get_objects(0)[-5:]:
            print(type(obj), repr(obj)[:60])

        print()
        print("obj", id(obj))
        print("remove", id(remove))

func()
gc.collect()