可选参数后的重载

Posted 2023-02-22

【中文标题】可选参数后的重载

【英文标题】：overload following optional argument

【发布时间】：2021-05-31 18:22:36

【问题描述】：

我有一个类Animal 和一个方法foo，它根据一个可选参数bar 后面的布尔参数inplace 具有不同的返回类型。我想重载该函数，以便在知道inplace 的值的情况下知道返回类型

这是我的代码：

# main.py

from __future__ import annotations

from typing import Optional, overload, Literal 


class Animal:
    @overload
    def foo(self, bar=..., inplace: Literal[False]=...) -> Animal:
        ...

    @overload
    def foo(self, bar=..., inplace: Literal[True]=...) -> None:
        ...

    def foo(
        self, bar=None, inplace: bool = False
    ) -> Optional[Animal]:
        ...


reveal_type(Animal().foo(bar='a'))
reveal_type(Animal().foo(inplace=True))
reveal_type(Animal().foo(inplace=False))

$ mypy main.py
main.py:8: error: Overloaded function signatures 1 and 2 overlap with incompatible return types
main.py:21: note: Revealed type is 'main.Animal'
main.py:22: note: Revealed type is 'None'
main.py:23: note: Revealed type is 'main.Animal'
Found 1 error in 1 file (checked 1 source file)

https://mypy-play.net/?mypy=latest&python=3.9&gist=49da369f6343543769eed2060fa61639

如何避免第 8 行出现 Overloaded function signatures 1 and 2 overlap with incompatible return types 错误？

【参考方案1】：

这似乎有效：

from __future__ import annotations

from typing import Optional, overload, Literal 


class Animal:

    # using defaults
    @overload
    def foo(self, bar=..., inplace: Literal[False]=...) -> Animal: ...

    # using inplace = True
    
    # with bar
    @overload
    def foo(self, bar, inplace: Literal[True]) -> None: ...

    # without bar
    @overload
    def foo(self, *, inplace: Literal[True]) -> None: ...

    # with bool
    @overload
    def foo(self, bar=..., inplace: bool=...) -> Optional[Animal]: ...

    def foo(
        self, bar=None, inplace = False
    ):
        ...


reveal_type(Animal().foo(bar='a'))
reveal_type(Animal().foo(bar='a', inplace=True))
reveal_type(Animal().foo(bar='a', inplace=False))
reveal_type(Animal().foo(inplace=True))
reveal_type(Animal().foo(inplace=False))
reveal_type(Animal().foo())

inplace: bool
reveal_type(Animal().foo(bar='a', inplace=inplace))
reveal_type(Animal().foo(inplace=inplace))

很多重载，但也许这在这里是不可避免的

【参考方案2】：

试试：

@overload
def foo(self, inplace: Literal[False]=..., bar=...) -> Animal:
    ...

@overload
def foo(self, inplace: Literal[True], bar=...,) -> None:
    ...

def foo(self, inplace=False, bar=None):
    ...

我更改了 args 的顺序，否则第二次重载不正确。

【讨论】：

我无法更改def foo 中的参数顺序，恐怕这将是一个重大更改