How do I make a custom class that's serializable with dataclasses.asdict()?

I'm trying to use a dataclass as a (more strongly typed) dictionary in my application, and found this strange behavior when using a custom type within the dataclass. I'm using Python 3.11.3 on Windows.

from dataclasses import dataclass, asdictclass CustomFloatList(list):    def __init__(self, args):        for i, arg in enumerate(args):            assert isinstance(arg, float), f"Expected index {i} to be a float, but it's a {type(arg).__name__}"        super().__init__(args)    @classmethod    def from_list(cls, l: list[float]):        return cls(l)@dataclassclass Poc:    x: CustomFloatListp = Poc(x=CustomFloatList.from_list([3.0]))print(p)  # Prints Poc(x=[3.0])print(p.x)  # Prints [3.0]print(asdict(p))  # Prints {'x': []}

This does not occur if I use a regular list[float], but I'm using a custom class here to enforce some runtime constraints.

How do I do this correctly?

I'm open to just using .__dict__ directly, but I thought asdict() was the more "official" way to handle this

A simple modification makes the code behave as expected, but is slightly less efficient:

from dataclasses import dataclass, asdictclass CustomFloatList(list):    def __init__(self, args):        dup_args = list(args)        for i, arg in enumerate(dup_args):            assert isinstance(arg, float), f"Expected index {i} to be a float, but it's a {type(arg).__name__}"        super().__init__(dup_args)    @classmethod    def from_list(cls, l: list[float]):        return cls(l)@dataclassclass Poc:    x: CustomFloatListp = Poc(x=CustomFloatList.from_list([3.0]))print(p)print(p.x)print(asdict(p))