如何在Python中对泛型类型使用isinstance

Question

我试图检查参数是否是类声明中指定的泛型类型的实例。然而，Python似乎不允许这样做

T = TypeVar('T')
class MyTypeChecker(Generic[T]):
    def is_right_type(self, x: Any):
        return isinstance(x, T)

这会产生错误'T' is a type variable and only valid in type context

Answer 1

您可以使用__orig_class__属性，但请记住，这是一个实现细节，在本answer中有更多细节

from typing import TypeVar, Generic, Any
T = TypeVar('T')


class MyTypeChecker(Generic[T]):
    def is_right_type(self, x: Any):
        return isinstance(x, self.__orig_class__.__args__[0])  # type: ignore


a = MyTypeChecker[int]()
b = MyTypeChecker[str]()

print(a.is_right_type(1))  # True
print(b.is_right_type(1))  # False
print(a.is_right_type('str'))  # False
print(b.is_right_type('str'))  # True