Python - An attempt to disable possibility to monkeypatch method (NOTE: This can't be done right; don't do this at home)

monkeypatch.py

class Person:
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return "Person: {}".format(self.name)

if __name__ == "__main__":
    def __str__(self):
        return "xoxoxo"
    
    Person.__str__ = __str__
    
    print(Person("Krzysztof"))

monkeypatch_disabled.py

class StrMonkeypatchDisabler(type):
    def __setattr__(self, key, value):
        if key != '__str__':
            print(
                "{cls}.__setattr__({key}, {value})"
                .format(cls=self.__class__.__name__, key=key, value=value)
            )
            super().__setattr__(key, value)
        else:
            print("Monkey patching '__str__' is disabled")

class Person(metaclass=StrMonkeypatchDisabler):
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return "Hello {}!".format(self.name)

    def __setattr__(self, key, value):
        print("Attempt to set {key}".format(key=key))
        
        if key != '__str__':
            super().__setattr__(key, value)
        else:
            print("You can't monkeypatch __str__!")

if __name__ == "__main__":
    def __str__(self):
        return "xoxoxo"
    
    p = Person("That works")
    p.__str__ = __str__
    print(p)
    
    Person.__str__ = __str__
    
    print(Person("Krzysztof"))

monkeypatch_first_thought.py

class Person:
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return "Person: {}".format(self.name)

    def __setattr__(self, key, value):
        print("Attempt to set {key}".format(key=key))
        
        if key != '__str__':
            super().__setattr__(key, value)
        else:
            print("You can't monkeypatch __str__!")

if __name__ == "__main__":
    def __str__(self):
        return "xoxoxo"
    
    p = Person("Almost working")
    p.__str__ = __str__
    print(p)
    
    Person.__str__ = __str__
    
    print(Person("Krzysztof"))