如何获取可调用返回值的注释文本？

Question

import inspect
from typing import Union

class ApiResponse: pass

class ApiWrapper():
    def send_message(self) -> Union[ApiResponse, str]:
        print(ApiWrapper._get_caller_method_return_type())

    @classmethod
    def _get_caller_method_return_type(cls):
        caller_method_name = inspect.stack()[1][3]
        return inspect.signature(getattr(cls, caller_method_name)).return_annotation

api = ApiWrapper()
api.send_message()

打印：

typing.Union[__main__.ApiResponse, str]

但是我想看到以下结果：

Union[ApiResponse, str]

如何获取可调用对象的返回值的注释文本（即字符串Union[ApiResponse, str]）？