Python 3.7数据类:将值赋给未定义的属性时引发错误

from dataclasses import dataclass

@dataclass
class MyClass:
    x: int
    y: int

obj = MyClass(1, 2)
obj.__dict__['z'] = 3  # 动态添加属性
print(obj.z)  # 输出: 3

from dataclasses import dataclass, field

@dataclass
class MyClass:
    x: int
    y: int
    z: dict = field(default_factory=dict)

obj = MyClass(1, 2)
obj.z['new_key'] = 'new_value'  # 动态修改属性
print(obj.z)  # 输出: {'new_key': 'new_value'}

from dataclasses import dataclass
from types import MappingProxyType

@dataclass
class MyClass:
    x: int
    y: int
    _extra: dict = field(default_factory=dict, repr=False)

    @property
    def extra(self):
        return MappingProxyType(self._extra)

obj = MyClass(1, 2)
obj._extra['new_key'] = 'new_value'  # 只能通过_extra修改
print(obj.extra)  # 输出: {'new_key': 'new_value'}