python - frozen=True 时如何设置__post_init__ 中dataclass 字段的值？

Question

我正在尝试创建一个卡住的数据类，但我在设置 __post_init__ 的值时遇到了问题。使用 frozen=True 设置时，是否可以根据 dataclass 中的 init param 的值设置字段值？

RANKS = '2,3,4,5,6,7,8,9,10,J,Q,K,A'.split(',')
SUITS = 'H,D,C,S'.split(',')


@dataclass(order=True, frozen=True)
class Card:
    rank: str = field(compare=False)
    suit: str = field(compare=False)
    value: int = field(init=False)
    def __post_init__(self):
        self.value = RANKS.index(self.rank) + 1
    def __add__(self, other):
        if isinstance(other, Card):
            return self.value + other.value
        return self.value + other
    def __str__(self):
        return f'{self.rank} of {self.suit}'

这是痕迹

 File "C:/Users/user/.PyCharm2018.3/config/scratches/scratch_5.py", line 17, in __post_init__
    self.value = RANKS.index(self.rank) + 1
  File "<string>", line 3, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field 'value'

Answer 1

使用the same thing the generated __init__ method does : object.__setattr__.

def __post_init__(self):
    object.__setattr__(self, 'value', RANKS.index(self.rank) + 1)