Creating a deepcopy of class instance with nested weakref to it

I have two classes: a parent class and a container class. The parent class instance has matching container class instance as a weak reference.

There is a problem while deep copying the parent instance, the weakref is still linking to the original instance. Here is a minimal example:

import weakref
from copy import deepcopy


class Container:    
    def __init__(self, parent):
        self.parent = weakref.ref(parent)


class Parent:
    def __init__(self):
        self.container = Container(self)


if __name__ == '__main__':
    parent1 = Parent()
    assert(parent1 is parent1.container.parent())

    parent2 = deepcopy(parent1)
    assert(parent2 is parent2.container.parent())

The second assertion fails.

I suspect that the __deepcopy__ magic method can be implemented, but not sure how exactly.