装饰器更改返回类型时的键入功能 [英] Typing function when decorator change return type

问题描述

如何为装饰器修改返回类型的函数正确编写类型?

how to correctly write types for the function whose return type is modified by decorator ?

简单例子:

def example_decorator(fn):
    def wrapper(data):
        res = fn(data)
        return ', '.join(res)

    return wrapper


@example_decorator
def func(data: list):  # -> ???? str ? list ?
    new_data = data
    new_data.append('XYZ')
    return new_data


# When we type func -> list

def test() -> str:
    result = func(['ABC', 'EFG'])
    print(type(result))  # <class 'str'>
    return result  # Incompatible return type [7]: Expected str but got list.


test()

推荐答案

可能是类型检查器的问题.解决方法如下.mypy 没问题，但 pycharm 和 pyre-check 有问题.

May be a typechecker problem. Solution below. With mypy its ok but pycharm and pyre-check is complaining.

from typing import *

def example_decorator(
    fn: Callable[[List[str]], List[str]]
) -> Callable[[List[str]], str]:
    def wrapper(data: List[str]) -> str:
        res = fn(data)
        return ', '.join(res)

    return wrapper


@example_decorator
def func(data: List[str]) -> List[str]:  
    data.append('XYZ')
    return data


def test() -> str:
    result = func(['ABC', 'EFG'])
    print(type(result))  # <class 'str'>
    return result


test()

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