报告 ClassVar 注解的无效用法。
示例:
from typing import ClassVar
class Cat:
color: ClassVar[str] = "white"
weight: int
def __init__(self, weight: int):
self.weight = weight
Cat.color = "black" # OK
my_cat = Cat(5)
my_cat.color = "gray" # 错误,在实例上设置类变量