I have a dataclass hierarchy:

@dataclass
class A:
    x: int
    y: int

@dataclass
class B(A):
    z: int = 1

Why is it that I can’t create B using an existing A directly?

a=A(0,0)
b=B(a) # exception

However, I can use __dict__

a=A(0,0)
b=B(**a.__dict__)

Is there a better way?