from dataclasses import dataclass
from io import BufferedRandom

@dataclass
class Shard:
    size: int
    file: BufferedRandom

    @staticmethod
    def load_shard(filename: str) -> 'Shard':
        file = open(filename, 'rb+')
        size = int.from_bytes(file.read(8), 'big')

        return Shard(size, file)

@dataclass
class Entry:
    shard: Shard

    content: bytearray



shart = Shard.load_shard('myfile')
print(shart.size)