How can you change the state of a class variable?

Question

Python

I have two scripts:
parent.py

class Test:
    def __init__(self):
        self.data = {
            'name': '',
            'password': ''
        }

    def fill_data(self):
        self.data["name"] = "John"
        self.data["password"] = "1234"

    def change_data(self, name):
        self.data["name"] = str(name)


new = Test()

if __name__ == "__main__":

    new.fill_data()
    time.sleep(5)
    print(new.data)

and child.py:

from parent import new

if __name__ == "__main__":
    print(f"[child]: Before change data is {new.data}") # тут должно выводится self.data = { 'name': 
    # 'John', 'password': '1234' }, а получается self.data = { 'name': "", 'password': "" }      
    setattr(new, 'name', 'Nick') # я также использовал просто new.data["name"] = "Nick"
    print(f"[child]: After change data is {new.data}")

The problem is that when you try to change the new object from child.py, nothing happens. As far as I understand, this is somehow related to class instances, but my knowledge is not yet enough to figure it out myself.

Answer 1

Well, nothing should have happened.
When you run child.py, you create an instance of the Test class, you have the data dictionary initialized ... That's it.
I know that you wanted the following to happen:

if __name__ == "__main__":
    new.fill_data()
    time.sleep(5)
    print(new.data)

But it doesn't work like that. The check is false. This works if you run parent.py directly:
And even more so, you just import the variable an instance of the Test class. Even if there was a while True loop, it wouldn't execute.
You tried to access new.data['name'] from child.py via setattr, but you did it wrong. You turned to new.name, that's the error. To do everything right through setattr, it was necessary to write: The answer, how to do it right, the child.py file

from parent import new

if __name__ == "__main__":
    new.fill_data()
    print(f"[child]: Before change data is {new.data}") # тут выведется правильная data  
    new.change_data('Nick')
    print(f"[child]: After change data is {new.data}")