How can I create a list attribute that updates dynamically in Python?

I have two classes that refer to each other in a one-to-many relationship (Kid and Toy in the below example). When I assign a new Toy to Kid, I want the Kid to be assigned to Toy as well.

Creating a custom class based on list for the toys attribute and redefining methods (e.g. append, extend, delete) would work but I wanted to know if there is a better way.

class Toy:
    def __init__(self, name, kid=None):
        self.name = name
        self.kid = kid

class Kid:
    def __init__(self, name, toys):
        self.name = name
        self.toys = toys

    @property
    def toys(self):
        return self._toys

    @toys.setter
    def toys(self, val):
        self._toys = val
        # Assign the kid to the toys
        for toy in self._toys:
            toy.kid = self

if __name__ == "__main__":
    toys = [Toy('Woodie'), Toy('Slinky'), Toy('Rex')]
    andy = Kid('Andy', toys)

    # Andy corrected assigned to toys
    for toy in andy.toys:
        print('{}\t{}'.format(toy.name, toy.kid.name))
    print('-')

    # Add new toy
    andy.toys.append(Toy('Buzz'))

    # Throws error because Buzz is not assigned Andy
    for toy in andy.toys:
        print('{}\t{}'.format(toy.name, toy.kid.name))

Output:

Woodie  Andy
Slinky  Andy
Rex     Andy
-
Woodie  Andy
Slinky  Andy
Rex     Andy
Traceback (most recent call last):
  File "c:/Users/jonat/Desktop/tests/inheritance_q.py", line 34, in <module>
    print('{}\t{}'.format(toy.name, toy.kid.name))
AttributeError: 'NoneType' object has no attribute 'name'

I would like Buzz to be assigned Andy.

You could just add a method into your Kid class:

class Toy:
    def __init__(self, name, kid=None):
        self.name = name
        self.kid = kid

class Kid:
    def __init__(self, name, toys):
        self.name = name
        self.toys = toys

    @property
    def toys(self):
        return self._toys

    @toys.setter
    def toys(self, val):
        self._toys = val
        # Assign the kid to the toys
        for toy in self._toys:
            toy.kid = self

    def give_toy(self, toy):
        toy.kid = self
        self.toys.append(toy)


if __name__ == "__main__":
    toys = [Toy('Woodie'), Toy('Slinky'), Toy('Rex')]
    andy = Kid('Andy', toys)

    # Andy corrected assigned to toys
    for toy in andy.toys:
        print('{}\t{}'.format(toy.name, toy.kid.name))
    print('-')

    # Add new toy
    andy.give_toy(Toy('Buzz'))

    # Throws error because Slinky is not assigned Andy
    for toy in andy.toys:
        print('{}\t{}'.format(toy.name, toy.kid.name))

Output:

Woodie  Andy
Slinky  Andy
Rex     Andy
-
Woodie  Andy
Slinky  Andy
Rex     Andy
Buzz    Andy