小编lap*_*ken的帖子

当处理 Python 数据类时，我遇到了这个很容易重现的奇怪错误。

from __future__ import annotations

import dataclasses as dc
import typing

@dc.dataclass
class Test:
    foo: dc.InitVar[int]

print(typing.get_type_hints(Test))

运行它会得到以下结果：

Traceback (most recent call last):
  File "test.py", line 11, in <module>
    print(typing.get_type_hints(Test))
  File "C:\Program Files\Python310\lib\typing.py", line 1804, in get_type_hints
    value = _eval_type(value, base_globals, base_locals)
  File "C:\Program Files\Python310\lib\typing.py", line 324, in _eval_type
    return t._evaluate(globalns, localns, recursive_guard)
  File "C:\Program Files\Python310\lib\typing.py", line 687, in _evaluate
    type_ =_type_check(
  File "C:\Program Files\Python310\lib\typing.py", line 173, in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
TypeError: Forward references must evaluate …

我对这种行为感到困惑：我有一个冻结的数据类，其中只需要 10 个，所以我想将它们放入枚举中，并且成功了。后来，我意识到我希望能够为它们命名，突然间，枚举无法实例化数据类。

import enum
import dataclasses as dc

class Stats(int, enum.Enum):
    HP = 0
    STA = 1
    SPD = 2
    ATK = 3
    DEF = 4
    SPATK = 5
    SPDEF = 6

@dc.dataclass(frozen=True)
class Strand:
    keeps: tuple[Stats, ...]
    costs: int

class Strands(Strand, enum.Enum):
    VIT =   ((Stats.HP,),              1000)
    END =   ((Stats.STA,),             1000)
    LTH =   ((Stats.SPD,),             1000)
    AGG =   ((Stats.ATK,),             1000)
    HRD =   ((Stats.DEF,),             1000)
    GFT =   ((Stats.SPATK,),           1000)
    DOM =   ((Stats.SPDEF,),           1000)
    VIGOR = ((Stats.HP, Stats.STA),    5000)
    MIGHT = ((Stats.ATK, …