need help with "can't get the length with Hand"

import random


class Die:
    def __init__(self, sides=2):
        if sides < 2:
            raise ValueError("Can't have fewer than two sides")
        self.sides = sides
        self.value = random.randint(1, sides)

    def __int__(self):
        return self.value

    def __add__(self, other):
        return int(self) + other

    def __radd__(self, other):
        return self + other

    def __repr__(self):
        return str(self.value)

    def __len__(self):
        return len(self)
class D20(Die):
    def __init__(self, *args, **kwargs):
        super().__init__(sides=20, *args, **kwargs)

from dice import D20

class Hand(list):
    def __init__(self, size=0, die_class=None, *args, **kwargs):
        if not die_class:
            raise ValueError("You must provide a die class")
        super().__init__()

        for _ in range(size):
            self.append(die_class())
        self.sort()
    @classmethod
    def roll(cls, size=2, die_class=D20):
        return cls(size=2, die_class=D20)
    @property
    def total(self):
        return sum(self)