metric-units.py

from dataclasses import dataclass
from enum import Enum

@dataclass(frozen=True)
class Scale:
    power: int
    suffix: str

class UnitSystem(Enum):
    IEC = 1024  # KiB, MiB...
    SI  = 1000  # kB, MB...

class Unit(Enum):
    B  = Scale(0, "B")
    KB = Scale(1, "KB")
    MB = Scale(2, "MB")
    GB = Scale(3, "GB")
    TB = Scale(4, "TB")
    PB = Scale(5, "PB")
    EB = Scale(6, "EB")
    ZB = Scale(7, "ZB")

    @property
    def power(self) -> int:
        return self.value.power

    @property
    def suffix(self) -> str:
        return self.value.suffix

    def factor(self, system: UnitSystem = UnitSystem.IEC) -> int:
        return int(system.value ** self.power)