装饰器的 Mypy 类型注释

如何解决装饰器的 Mypy 类型注释

我有一个装饰器类，但无法为其添加类型注释。

import functools

class LogInfo:

    def __init__(self,environment: str):
        self.environment = environment

    def __call__(self,func):
        @functools.wraps(func)
        def decorated(*args,**kwargs):
            # My Stuff goes here...
            return func(*args,**kwargs)
        return decorated

我能得到的最接近的是：

import functools
from collections import Callable
from typing import TypeVar,Any

GenericReturn = TypeVar("GenericReturn")
GenericCallable = TypeVar("GenericCallable",bound=Callable[...,GenericReturn])


class LogInfo:
    def __init__(self,environment: str) -> None:
        self.environment = environment

    def __call__(self,func: GenericCallable) -> GenericCallable:
        @functools.wraps(func)
        def decorated(*args: Any,**kwargs: Any) -> GenericReturn:
            # My Stuff goes here...
            return func(*args,**kwargs)
        return decorated  # LINE 29

但我仍然收到此错误：

29: error: Incompatible return value type (got "Callable[...,Any]",expected "GenericCallable")

删除 @functools.wraps(func) 会将错误更改为：

29: error: Incompatible return value type (got "Callable[[Vararg(Any),KwArg(Any)],GenericReturn]",expected "GenericCallable")

解决方法

这是一个不错的解决方案：

import functools
from collections import Callable
from typing import TypeVar,cast,Any

T = TypeVar("T",bound=Callable[...,Any])


class LogInfo:
    def __init__(self,environment: str):
        self.environment = environment

    def __call__(self,func: T) -> T:
        @functools.wraps(func)
        def decorated(*args,**kwargs):  # type: ignore
            # My Stuff goes here...
            return func(*args,**kwargs)

        return cast(T,decorated)

我们可以使用以下代码进行测试：

@LogInfo(environment="HI")
def foo(input: str) -> str:
    return f"{input}{input}"

# NOTE: Intentional error here to trigger mypy
def bar() -> int:
    return foo("jake")

正如预期的那样，我们收到此 mypy 错误：

error: Incompatible return value type (got "str",expected "int")

还有待改进的地方：

• return cast(T,decorated) 很丑。
• 输入 args 和 kwargs 会很好。