Python dataclass initialization and updating its field

Question

I just started learning Python and have a question about dataclass initialization and updating its field using a function.

When I run the code below, I was expecting to second.flags.checked to be None, but I see it set to True instead. What is the correct way to initialize a dataclass so that new Flags is initialized I create a new TestClass in this case?

class Flags:
    checked: bool = None


@dataclass
class TestClass:
    test: str
    flags: Flags = Flags()

    def update_flags(self):
        self.flags.checked = True


first = TestClass(test="test1")
first.update_flags()

second = TestClass(test="test2")
print(f"{second.flags.checked}")