`unittest.mock.patch` and `unittest.mock.patch.object` are wrongly typed when new_callable is provided

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難度
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預估耗時
1-2 天
新手友好度
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Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
停滯
技術堆疊
python
領域
testing

研究方向

檢查 issue 中顯示的 unittest.mock.patch 和 patch.object 多載，然後找到它們的 typeshed stub 和相關測試。檢查預設 patching、new、new_callable，以及不可呼叫的 new_callable 情況下推斷出的型別；完成的標準是兩個 API 都只接受可呼叫的 factory，並正確推斷所建立物件的型別。

由索引模型根據 Issue 內容生成。

描述

Steps to reproduce

from unittest.mock import patch


class NewPrinter:
    pass


with patch("pprint.PrettyPrinter", new_callable=lambda: NewPrinter) as patched_printer:
    print(patched_printer)  # <class '__main__.NewPrinter'>
    reveal_type(patched_printer)  # "Union[unittest.mock.MagicMock, unittest.mock.AsyncMock]"

Same deal with unittest.mock.patch.object

from unittest.mock import patch
import pprint

class NewPrinter:
    ...


with patch.object(pprint, "PrettyPrinter", new_callable=lambda: NewPrinter) as patched_printer:
    print(patched_printer)  # <class '__main__.NewPrinter'>
    reveal_type(patched_printer)  # "Union[unittest.mock.MagicMock, unittest.mock.AsyncMock]"

Suggested fix

We discuss unittest.mock.patch in the following, but the same principles apply to unittest.mock.patch.object too

Current signatures:

    @overload
    def __call__(
        self,
        target: str,
        new: _T,
        spec: Any | None = ...,
        create: bool = ...,
        spec_set: Any | None = ...,
        autospec: Any | None = ...,
        new_callable: Any | None = ...,
        **kwargs: Any,
    ) -> _patch[_T]: ...
    @overload
    def __call__(
        self,
        target: str,
        *,
        spec: Any | None = ...,
        create: bool = ...,
        spec_set: Any | None = ...,
        autospec: Any | None = ...,
        new_callable: Any | None = ...,
        **kwargs: Any,
    ) -> _patch_default_new: ...

There are 2 problems here:

  • new_callable shouldn't be Any | None in the first place, it should only accept Callable| None, as the it will raise if the provided value is not a callable 
    with patch("pprint.PrettyPrinter", new_callable=1) as patched_printer:  # TypeError: 'int' object is not callable
  • Need to differentiate the case where new_callable is provided and left as default None
    • When new_callable: Callable[..., T], returns _patch[_T]
    • When new_callable: None = ..., returns _patch_default_new

Seems like this would do the job:

    @overload
    def __call__(
        self,
        target: str,
        new: _T,
        spec: Any | None = ...,
        create: bool = ...,
        spec_set: Any | None = ...,
        autospec: Any | None = ...,
        new_callable: Callable[..., Any] | None = ...,
        **kwargs: Any,
    ) -> _patch[_T]: ...
    @overload
    def __call__(
        self,
        target: str,
        *,
        spec: Any | None = ...,
        create: bool = ...,
        spec_set: Any | None = ...,
        autospec: Any | None = ...,
        new_callable: Callable[..., _T],
        **kwargs: Any,
    ) -> _patch[_T]
    @overload
    def __call__(
        self,
        target: str,
        *,
        spec: Any | None = ...,
        create: bool = ...,
        spec_set: Any | None = ...,
        autospec: Any | None = ...,
        new_callable: None = ...,
        **kwargs: Any,
    ) -> _patch_default_new: ...

Testing results

from unittest.mock import patch


class NewPrinter:
    pass


with patch("pprint.PrettyPrinter") as patched_printer:
    print(patched_printer)  # <MagicMock name='PrettyPrinter' id='125908774402896'>
    reveal_type(patched_printer)  # MagicMock | AsyncMock


with patch("pprint.PrettyPrinter", new=NewPrinter) as patched_printer:
    print(patched_printer)  # <class '__main__.NewPrinter'>
    reveal_type(patched_printer)  # type[NewPrinter]


with patch("pprint.PrettyPrinter", new_callable=lambda: NewPrinter) as patched_printer:
    print(patched_printer)  # <class '__main__.NewPrinter'>
    reveal_type(patched_printer)  # type[NewPrinter]


# No overload variant matches for non-callable type
with patch("pprint.PrettyPrinter", new_callable="non-callable") as patched_printer:
    ...

Haven't tried unittest.mock.patch.object yet, but probably same thing

Would be great to see what the maintainers think.

I'll dig deeper and try to open a PR, maybe this weekend, will be my first PR in typeshed :)

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